Help getting an LCD to work

W

Will

Guest
I have an Optrex LCD (DMC-20481NY-LY-AGE) that is 4x20 characters and
driven by a Microchip PIC16F877 running at 20MHz. I know I got this
exact same physical LCD to work before but for the life of me I can't
recall what trick I used to do so. Attached at the end is my
software. I get power to the LCD, but all I see is lines 1 and 3 as
all dark and lines 2 and 4 as all clear. Hunting around newsgroups
leads me to think my initialization routines aren't working (gee, ya
think?!?!) but as near as I can tell I have met or exceeded all of the
timing requirements for data transfer. PLEASE HELP!!!!! If it
matters, I am using a dedicated 5V DC supply to drive both the PIC and
the LCD. The PIC is connected to the LCD through 330 Ohm resistors,
with 10KOhm pulldown resistors to ground on ALL of the lines on the
PIC side. This was because I was seeing a lot of glitches on powerup
due to ports being inputs. Each line also has a .01uF cap to ground
and there is a bypass capacitor on the 5V line to ground next to the
PIC. The BusyFlag is also connected directly from the LCD to the PIC
on PORTB, 6. Thanks for any insight!
-Will

; LCD Control Software
;
; Software uses a 20MHz crystal
; for timing.
;

;******************************************************************
Stall MACRO
LOCAL Stall_Jump
goto Stall_Jump
Stall_Jump
ENDM
;******************************************************************
Wait_For_Busy_Flag MACRO
btfsc BUSY_FLAG
goto $-1
ENDM
;******************************************************************
Wait_15ms MACRO
LOCAL OuterLoop
LOCAL InnerLoop

movlw .59
movwf OUTER_COUNTER
OuterLoop
movlw .255
movwf INNER_COUNTER
InnerLoop
Stall
decfsz INNER_COUNTER, F
goto InnerLoop
decfsz OUTER_COUNTER, F
goto OuterLoop
ENDM
;******************************************************************
Wait_4.1ms MACRO
LOCAL OuterLoop
LOCAL InnerLoop

movlw .17
movwf OUTER_COUNTER
OuterLoop
movlw .255
movwf INNER_COUNTER
InnerLoop
Stall
decfsz INNER_COUNTER, F
goto InnerLoop
decfsz OUTER_COUNTER, F
goto OuterLoop
ENDM
;******************************************************************
Wait_100us MACRO
LOCAL InnerLoop

movlw .100
movwf INNER_COUNTER
InnerLoop
Stall
decfsz INNER_COUNTER, F
goto InnerLoop
ENDM
;******************************************************************

list p=16F877

; Include file, change directory if needed
include "p16f877.inc"

#define ENABLE PORTE, 2
#define RS PORTE, 1
#define RW PORTE, 0

#define DATA_PORT PORTD
#define BUSY_FLAG PORTB, 6

OUTER_COUNTER equ 0x20
INNER_COUNTER equ 0x21


W_TEMP equ 0x70
STATUS_TEMP equ 0x71
PCLATH_TEMP equ 0x72


;//Reset Vector
Org 0x00
clrf PCLATH ; ensure page bits are cleared
goto Initialize

;//Interrupt Vector
ORG 0x04
MOVWF W_TEMP ;Copy W to TEMP register
SWAPF STATUS,W ;Swap status to be saved into W
CLRF STATUS ;bank 0, regardless of current bank, Clears
IRP,RP1,RP0
MOVWF STATUS_TEMP ;Save status to bank zero STATUS_TEMP
register
MOVF PCLATH, W ;Only required if using pages 1, 2 and/or 3
MOVWF PCLATH_TEMP ;Save PCLATH into W
CLRF PCLATH ;Page zero, regardless of current page

;Fill this in if you want interrupt vectoring

banksel PCLATH_TEMP
MOVF PCLATH_TEMP, W ;Restore PCLATH
MOVWF PCLATH ;Move W into PCLATH
SWAPF STATUS_TEMP,W ;Swap STATUS_TEMP register into W
;(sets bank to original state)
MOVWF STATUS ;Move W into STATUS register
SWAPF W_TEMP,F ;Swap W_TEMP
SWAPF W_TEMP,W ;Swap W_TEMP into W
retfie ; return from interrupt

;//Initialization
Initialize
clrf INTCON
clrf INTCON
CGIE
bcf INTCON, GIE
btfsc INTCON, GIE
goto CGIE

; //Declare port/pin definitions
banksel TRISA
movlw B'00000111'
movwf ADCON1 ; Port A is all digital
movlw B'00000000'
movwf TRISA ; Port A is OOOOOOOO
movlw B'01000000'
movwf TRISB ; Port B is OIOOOOOO
movlw B'10000001'
movwf TRISC ; Port C is IOOOOOOI
movlw B'00000000'
movwf TRISD ; Port D is OOOOOOOO
bcf TRISE, PSPMODE ; Turn off the parallel port
bcf TRISE, 0 ; Port E is -----OOO
bcf TRISE, 1
bcf TRISE, 2

bsf OPTION_REG, 7 ;Turn off port B pullups

banksel OUTER_COUNTER
bsf PORTB, 7

Wait_15ms
Wait_15ms

bcf PORTB, 7

bcf RS
bcf RW
movlw b'00111000'
call StrobeData

Wait_4.1ms
Wait_4.1ms

bcf RS
bcf RW
movlw b'00111000'
call StrobeData

Wait_4.1ms
Wait_4.1ms

bcf RS
bcf RW
movlw b'00111000'
call StrobeData

Wait_4.1ms
Wait_4.1ms

call DisplayOFF_CursorOFF_BlinkOFF
Wait_15ms
Wait_4.1ms

call DisplayON_CursorON_BlinkON
Wait_15ms
Wait_4.1ms

call EntryModeSet
Wait_100us

call ClearDisplay
Wait_15ms
Wait_4.1ms

movlw b'01001000' ;H
call SendChar
movlw b'01100101' ;e
call SendChar
movlw b'01101100' ;l
call SendChar
movlw b'01101100' ;l
call SendChar
movlw b'01101111' ;o
call SendChar
movlw b'01010111' ;W
call SendChar
movlw b'01101111' ;o
call SendChar
movlw b'01110010' ;r
call SendChar
movlw b'01101100' ;l
call SendChar
movlw b'01100100' ;d
call SendChar

Eternal
bcf PORTB, 0
nop
bsf PORTB, 0
goto Eternal

;-----------
StrobeData
nop
bsf ENABLE
nop
movwf DATA_PORT
nop
bcf ENABLE
return
;-----------
EntryModeSet
btfsc BUSY_FLAG
goto EntryModeSet
bcf RS
bcf RW
movlw b'00000110'
call StrobeData
return
;-----------
SendChar
btfsc BUSY_FLAG
goto SendChar
bsf RS
bcf RW
call StrobeData
return
;-----------
ClearDisplay
btfsc BUSY_FLAG
goto ClearDisplay
bcf RS
bcf RW
movlw 0x01
call StrobeData
return
;-----------
HomeCursor
btfsc BUSY_FLAG
goto HomeCursor
bcf RS
bcf RW
movlw 0x02
call StrobeData
return
;-----------
DisplayOFF_CursorOFF_BlinkOFF
btfsc BUSY_FLAG
goto DisplayOFF_CursorOFF_BlinkOFF
bcf RS
bcf RW
movlw b'00001000'
call StrobeData
return
;-----------
DisplayOFF_CursorOFF_BlinkON
btfsc BUSY_FLAG
goto DisplayOFF_CursorOFF_BlinkON
bcf RS
bcf RW
movlw b'00001001'
call StrobeData
return
;-----------
DisplayOFF_CursorON_BlinkOFF
btfsc BUSY_FLAG
goto DisplayOFF_CursorON_BlinkOFF
bcf RS
bcf RW
movlw b'00001010'
call StrobeData
return
;-----------
DisplayOFF_CursorON_BlinkON
btfsc BUSY_FLAG
goto DisplayOFF_CursorON_BlinkON
bcf RS
bcf RW
movlw b'00001011'
call StrobeData
return
;-----------
DisplayON_CursorOFF_BlinkOFF
btfsc BUSY_FLAG
goto DisplayON_CursorOFF_BlinkOFF
bcf RS
bcf RW
movlw b'00001100'
call StrobeData
return
;-----------
DisplayON_CursorOFF_BlinkON
btfsc BUSY_FLAG
goto DisplayON_CursorOFF_BlinkON
bcf RS
bcf RW
movlw b'00001101'
call StrobeData
return
;-----------
DisplayON_CursorON_BlinkOFF
btfsc BUSY_FLAG
goto DisplayON_CursorON_BlinkOFF
bcf RS
bcf RW
movlw b'00001110'
call StrobeData
return
;-----------
DisplayON_CursorON_BlinkON
btfsc BUSY_FLAG
goto DisplayON_CursorON_BlinkON
bcf RS
bcf RW
movlw b'00001111'
call StrobeData
return
;-----------
END
 
Will wrote:

I have an Optrex LCD (DMC-20481NY-LY-AGE) that is 4x20 characters and
driven by a Microchip PIC16F877 running at 20MHz. I know I got this
exact same physical LCD to work before but for the life of me I can't
recall what trick I used to do so. Attached at the end is my
software. I get power to the LCD, but all I see is lines 1 and 3 as
all dark and lines 2 and 4 as all clear. Hunting around newsgroups
leads me to think my initialization routines aren't working (gee, ya
think?!?!) but as near as I can tell I have met or exceeded all of the
timing requirements for data transfer. PLEASE HELP!!!!! If it
matters, I am using a dedicated 5V DC supply to drive both the PIC and
the LCD. The PIC is connected to the LCD through 330 Ohm resistors,
with 10KOhm pulldown resistors to ground on ALL of the lines on the
PIC side. This was because I was seeing a lot of glitches on powerup
due to ports being inputs. Each line also has a .01uF cap to ground
and there is a bypass capacitor on the 5V line to ground next to the
PIC. The BusyFlag is also connected directly from the LCD to the PIC
on PORTB, 6. Thanks for any insight!
[...]
Click to expand...

10nF on each signal line is quite a lot! Why do you need such a big
capacitive load on the data wires?

Have you checked the timing on a scope, or are you just counting clock
cycles in your program?

--
Cheers
Stefan
 
Make sure you have the proper delays in the Init routines.
I've used the same display and had problems with short delays in the Init routines.

Cheers

"Will" <larkmore@aol.com> wrote in message news:5faf6114.0402031434.38db8ce2@posting.google.com...
I have an Optrex LCD (DMC-20481NY-LY-AGE) that is 4x20 characters and
driven by a Microchip PIC16F877 running at 20MHz. I know I got this
exact same physical LCD to work before but for the life of me I can't
recall what trick I used to do so. Attached at the end is my
software. I get power to the LCD, but all I see is lines 1 and 3 as
all dark and lines 2 and 4 as all clear. Hunting around newsgroups
leads me to think my initialization routines aren't working (gee, ya
think?!?!) but as near as I can tell I have met or exceeded all of the
timing requirements for data transfer. PLEASE HELP!!!!! If it
matters, I am using a dedicated 5V DC supply to drive both the PIC and
the LCD. The PIC is connected to the LCD through 330 Ohm resistors,
with 10KOhm pulldown resistors to ground on ALL of the lines on the
PIC side. This was because I was seeing a lot of glitches on powerup
due to ports being inputs. Each line also has a .01uF cap to ground
and there is a bypass capacitor on the 5V line to ground next to the
PIC. The BusyFlag is also connected directly from the LCD to the PIC
on PORTB, 6. Thanks for any insight!
-Will

; LCD Control Software
;
; Software uses a 20MHz crystal
; for timing.
;

;******************************************************************
Stall MACRO
LOCAL Stall_Jump
goto Stall_Jump
Stall_Jump
ENDM
;******************************************************************
Wait_For_Busy_Flag MACRO
btfsc BUSY_FLAG
goto $-1
ENDM
;******************************************************************
Wait_15ms MACRO
LOCAL OuterLoop
LOCAL InnerLoop

movlw .59
movwf OUTER_COUNTER
OuterLoop
movlw .255
movwf INNER_COUNTER
InnerLoop
Stall
decfsz INNER_COUNTER, F
goto InnerLoop
decfsz OUTER_COUNTER, F
goto OuterLoop
ENDM
;******************************************************************
Wait_4.1ms MACRO
LOCAL OuterLoop
LOCAL InnerLoop

movlw .17
movwf OUTER_COUNTER
OuterLoop
movlw .255
movwf INNER_COUNTER
InnerLoop
Stall
decfsz INNER_COUNTER, F
goto InnerLoop
decfsz OUTER_COUNTER, F
goto OuterLoop
ENDM
;******************************************************************
Wait_100us MACRO
LOCAL InnerLoop

movlw .100
movwf INNER_COUNTER
InnerLoop
Stall
decfsz INNER_COUNTER, F
goto InnerLoop
ENDM
;******************************************************************

list p=16F877

; Include file, change directory if needed
include "p16f877.inc"

#define ENABLE PORTE, 2
#define RS PORTE, 1
#define RW PORTE, 0

#define DATA_PORT PORTD
#define BUSY_FLAG PORTB, 6

OUTER_COUNTER equ 0x20
INNER_COUNTER equ 0x21


W_TEMP equ 0x70
STATUS_TEMP equ 0x71
PCLATH_TEMP equ 0x72


;//Reset Vector
Org 0x00
clrf PCLATH ; ensure page bits are cleared
goto Initialize

;//Interrupt Vector
ORG 0x04
MOVWF W_TEMP ;Copy W to TEMP register
SWAPF STATUS,W ;Swap status to be saved into W
CLRF STATUS ;bank 0, regardless of current bank, Clears
IRP,RP1,RP0
MOVWF STATUS_TEMP ;Save status to bank zero STATUS_TEMP
register
MOVF PCLATH, W ;Only required if using pages 1, 2 and/or 3
MOVWF PCLATH_TEMP ;Save PCLATH into W
CLRF PCLATH ;Page zero, regardless of current page

;Fill this in if you want interrupt vectoring

banksel PCLATH_TEMP
MOVF PCLATH_TEMP, W ;Restore PCLATH
MOVWF PCLATH ;Move W into PCLATH
SWAPF STATUS_TEMP,W ;Swap STATUS_TEMP register into W
;(sets bank to original state)
MOVWF STATUS ;Move W into STATUS register
SWAPF W_TEMP,F ;Swap W_TEMP
SWAPF W_TEMP,W ;Swap W_TEMP into W
retfie ; return from interrupt

;//Initialization
Initialize
clrf INTCON
clrf INTCON
CGIE
bcf INTCON, GIE
btfsc INTCON, GIE
goto CGIE

; //Declare port/pin definitions
banksel TRISA
movlw B'00000111'
movwf ADCON1 ; Port A is all digital
movlw B'00000000'
movwf TRISA ; Port A is OOOOOOOO
movlw B'01000000'
movwf TRISB ; Port B is OIOOOOOO
movlw B'10000001'
movwf TRISC ; Port C is IOOOOOOI
movlw B'00000000'
movwf TRISD ; Port D is OOOOOOOO
bcf TRISE, PSPMODE ; Turn off the parallel port
bcf TRISE, 0 ; Port E is -----OOO
bcf TRISE, 1
bcf TRISE, 2

bsf OPTION_REG, 7 ;Turn off port B pullups

banksel OUTER_COUNTER
bsf PORTB, 7

Wait_15ms
Wait_15ms

bcf PORTB, 7

bcf RS
bcf RW
movlw b'00111000'
call StrobeData

Wait_4.1ms
Wait_4.1ms

bcf RS
bcf RW
movlw b'00111000'
call StrobeData

Wait_4.1ms
Wait_4.1ms

bcf RS
bcf RW
movlw b'00111000'
call StrobeData

Wait_4.1ms
Wait_4.1ms

call DisplayOFF_CursorOFF_BlinkOFF
Wait_15ms
Wait_4.1ms

call DisplayON_CursorON_BlinkON
Wait_15ms
Wait_4.1ms

call EntryModeSet
Wait_100us

call ClearDisplay
Wait_15ms
Wait_4.1ms

movlw b'01001000' ;H
call SendChar
movlw b'01100101' ;e
call SendChar
movlw b'01101100' ;l
call SendChar
movlw b'01101100' ;l
call SendChar
movlw b'01101111' ;o
call SendChar
movlw b'01010111' ;W
call SendChar
movlw b'01101111' ;o
call SendChar
movlw b'01110010' ;r
call SendChar
movlw b'01101100' ;l
call SendChar
movlw b'01100100' ;d
call SendChar

Eternal
bcf PORTB, 0
nop
bsf PORTB, 0
goto Eternal

;-----------
StrobeData
nop
bsf ENABLE
nop
movwf DATA_PORT
nop
bcf ENABLE
return
;-----------
EntryModeSet
btfsc BUSY_FLAG
goto EntryModeSet
bcf RS
bcf RW
movlw b'00000110'
call StrobeData
return
;-----------
SendChar
btfsc BUSY_FLAG
goto SendChar
bsf RS
bcf RW
call StrobeData
return
;-----------
ClearDisplay
btfsc BUSY_FLAG
goto ClearDisplay
bcf RS
bcf RW
movlw 0x01
call StrobeData
return
;-----------
HomeCursor
btfsc BUSY_FLAG
goto HomeCursor
bcf RS
bcf RW
movlw 0x02
call StrobeData
return
;-----------
DisplayOFF_CursorOFF_BlinkOFF
btfsc BUSY_FLAG
goto DisplayOFF_CursorOFF_BlinkOFF
bcf RS
bcf RW
movlw b'00001000'
call StrobeData
return
;-----------
DisplayOFF_CursorOFF_BlinkON
btfsc BUSY_FLAG
goto DisplayOFF_CursorOFF_BlinkON
bcf RS
bcf RW
movlw b'00001001'
call StrobeData
return
;-----------
DisplayOFF_CursorON_BlinkOFF
btfsc BUSY_FLAG
goto DisplayOFF_CursorON_BlinkOFF
bcf RS
bcf RW
movlw b'00001010'
call StrobeData
return
;-----------
DisplayOFF_CursorON_BlinkON
btfsc BUSY_FLAG
goto DisplayOFF_CursorON_BlinkON
bcf RS
bcf RW
movlw b'00001011'
call StrobeData
return
;-----------
DisplayON_CursorOFF_BlinkOFF
btfsc BUSY_FLAG
goto DisplayON_CursorOFF_BlinkOFF
bcf RS
bcf RW
movlw b'00001100'
call StrobeData
return
;-----------
DisplayON_CursorOFF_BlinkON
btfsc BUSY_FLAG
goto DisplayON_CursorOFF_BlinkON
bcf RS
bcf RW
movlw b'00001101'
call StrobeData
return
;-----------
DisplayON_CursorON_BlinkOFF
btfsc BUSY_FLAG
goto DisplayON_CursorON_BlinkOFF
bcf RS
bcf RW
movlw b'00001110'
call StrobeData
return
;-----------
DisplayON_CursorON_BlinkON
btfsc BUSY_FLAG
goto DisplayON_CursorON_BlinkON
bcf RS
bcf RW
movlw b'00001111'
call StrobeData
return
;-----------
END
Click to expand...
 
I can only tell you from my experience which things made my life difficult
with LCD.

1. Contrast voltage had to be negative.

I belive it isn't the case in your case, you only have to connect 10k
potentiometer
for contrast.

2. Inpropper initialization routine.

Wrong sequence of initialization commands. If order off commands is not
right it
can cause a lot of headaches.

3. Using BUSY flag?

When using BUSY flag you have to watch carefuly during the initialization
routine
when the busy flag can be checked.

In your case my guess you would be you have incorrect initialization routine
maybe
timings are ok but the order of commands isn't.
I had done initialization as written in one datasheet of my 2x16 LCD, and it
worked
badly sometimes it would initialize the LCD, and sometimes wouldn't I found
another
sequence for initializing on the Internet and it worked great since then.

Mickey
 
"Will" <larkmore@aol.com> wrote in message
news:5faf6114.0402031434.38db8ce2@posting.google.com...
I have an Optrex LCD (DMC-20481NY-LY-AGE) that is 4x20 characters and
driven by a Microchip PIC16F877 running at 20MHz. I know I got this
exact same physical LCD to work before but for the life of me I can't
recall what trick I used to do so. Attached at the end is my
software. I get power to the LCD, but all I see is lines 1 and 3 as
all dark and lines 2 and 4 as all clear. Hunting around newsgroups
leads me to think my initialization routines aren't working (gee, ya
think?!?!) but as near as I can tell I have met or exceeded all of the
timing requirements for data transfer. PLEASE HELP!!!!! If it
matters, I am using a dedicated 5V DC supply to drive both the PIC and
the LCD. The PIC is connected to the LCD through 330 Ohm resistors,
with 10KOhm pulldown resistors to ground on ALL of the lines on the
PIC side. This was because I was seeing a lot of glitches on powerup
due to ports being inputs. Each line also has a .01uF cap to ground
and there is a bypass capacitor on the 5V line to ground next to the
PIC. The BusyFlag is also connected directly from the LCD to the PIC
on PORTB, 6. Thanks for any insight!
-Will
Click to expand...
Your strobedata routine is too fast. Many LCD displays have a cycle time of
500ns to 1000ns, where the E has to be kept high for 300 to 500ns or longer.
Apart from that, your filtering of the datalines kills your signals. 0.01uF
and 330 Ohm has a time constant of 3.3us. Your signals in the order of 1us
cycle times will NEVER pass this filter. Remove the caps and resistors and
you'll be fine.

Meindert
 
Have a look at this very usfull sofware pic simulator including lcd
http://www.oshonsoft.com/pic.html
regards
bob
"Will" <larkmore@aol.com> wrote in message
news:5faf6114.0402031434.38db8ce2@posting.google.com...
I have an Optrex LCD (DMC-20481NY-LY-AGE) that is 4x20 characters and
driven by a Microchip PIC16F877 running at 20MHz. I know I got this
exact same physical LCD to work before but for the life of me I can't
recall what trick I used to do so. Attached at the end is my
software. I get power to the LCD, but all I see is lines 1 and 3 as
all dark and lines 2 and 4 as all clear. Hunting around newsgroups
leads me to think my initialization routines aren't working (gee, ya
think?!?!) but as near as I can tell I have met or exceeded all of the
timing requirements for data transfer. PLEASE HELP!!!!! If it
matters, I am using a dedicated 5V DC supply to drive both the PIC and
the LCD. The PIC is connected to the LCD through 330 Ohm resistors,
with 10KOhm pulldown resistors to ground on ALL of the lines on the
PIC side. This was because I was seeing a lot of glitches on powerup
due to ports being inputs. Each line also has a .01uF cap to ground
and there is a bypass capacitor on the 5V line to ground next to the
PIC. The BusyFlag is also connected directly from the LCD to the PIC
on PORTB, 6. Thanks for any insight!
-Will

; LCD Control Software
;
; Software uses a 20MHz crystal
; for timing.
;

;******************************************************************
Stall MACRO
LOCAL Stall_Jump
goto Stall_Jump
Stall_Jump
ENDM
;******************************************************************
Wait_For_Busy_Flag MACRO
btfsc BUSY_FLAG
goto $-1
ENDM
;******************************************************************
Wait_15ms MACRO
LOCAL OuterLoop
LOCAL InnerLoop

movlw .59
movwf OUTER_COUNTER
OuterLoop
movlw .255
movwf INNER_COUNTER
InnerLoop
Stall
decfsz INNER_COUNTER, F
goto InnerLoop
decfsz OUTER_COUNTER, F
goto OuterLoop
ENDM
;******************************************************************
Wait_4.1ms MACRO
LOCAL OuterLoop
LOCAL InnerLoop

movlw .17
movwf OUTER_COUNTER
OuterLoop
movlw .255
movwf INNER_COUNTER
InnerLoop
Stall
decfsz INNER_COUNTER, F
goto InnerLoop
decfsz OUTER_COUNTER, F
goto OuterLoop
ENDM
;******************************************************************
Wait_100us MACRO
LOCAL InnerLoop

movlw .100
movwf INNER_COUNTER
InnerLoop
Stall
decfsz INNER_COUNTER, F
goto InnerLoop
ENDM
;******************************************************************

list p=16F877

; Include file, change directory if needed
include "p16f877.inc"

#define ENABLE PORTE, 2
#define RS PORTE, 1
#define RW PORTE, 0

#define DATA_PORT PORTD
#define BUSY_FLAG PORTB, 6

OUTER_COUNTER equ 0x20
INNER_COUNTER equ 0x21


W_TEMP equ 0x70
STATUS_TEMP equ 0x71
PCLATH_TEMP equ 0x72


;//Reset Vector
Org 0x00
clrf PCLATH ; ensure page bits are cleared
goto Initialize

;//Interrupt Vector
ORG 0x04
MOVWF W_TEMP ;Copy W to TEMP register
SWAPF STATUS,W ;Swap status to be saved into W
CLRF STATUS ;bank 0, regardless of current bank, Clears
IRP,RP1,RP0
MOVWF STATUS_TEMP ;Save status to bank zero STATUS_TEMP
register
MOVF PCLATH, W ;Only required if using pages 1, 2 and/or 3
MOVWF PCLATH_TEMP ;Save PCLATH into W
CLRF PCLATH ;Page zero, regardless of current page

;Fill this in if you want interrupt vectoring

banksel PCLATH_TEMP
MOVF PCLATH_TEMP, W ;Restore PCLATH
MOVWF PCLATH ;Move W into PCLATH
SWAPF STATUS_TEMP,W ;Swap STATUS_TEMP register into W
;(sets bank to original state)
MOVWF STATUS ;Move W into STATUS register
SWAPF W_TEMP,F ;Swap W_TEMP
SWAPF W_TEMP,W ;Swap W_TEMP into W
retfie ; return from interrupt

;//Initialization
Initialize
clrf INTCON
clrf INTCON
CGIE
bcf INTCON, GIE
btfsc INTCON, GIE
goto CGIE

; //Declare port/pin definitions
banksel TRISA
movlw B'00000111'
movwf ADCON1 ; Port A is all digital
movlw B'00000000'
movwf TRISA ; Port A is OOOOOOOO
movlw B'01000000'
movwf TRISB ; Port B is OIOOOOOO
movlw B'10000001'
movwf TRISC ; Port C is IOOOOOOI
movlw B'00000000'
movwf TRISD ; Port D is OOOOOOOO
bcf TRISE, PSPMODE ; Turn off the parallel port
bcf TRISE, 0 ; Port E is -----OOO
bcf TRISE, 1
bcf TRISE, 2

bsf OPTION_REG, 7 ;Turn off port B pullups

banksel OUTER_COUNTER
bsf PORTB, 7

Wait_15ms
Wait_15ms

bcf PORTB, 7

bcf RS
bcf RW
movlw b'00111000'
call StrobeData

Wait_4.1ms
Wait_4.1ms

bcf RS
bcf RW
movlw b'00111000'
call StrobeData

Wait_4.1ms
Wait_4.1ms

bcf RS
bcf RW
movlw b'00111000'
call StrobeData

Wait_4.1ms
Wait_4.1ms

call DisplayOFF_CursorOFF_BlinkOFF
Wait_15ms
Wait_4.1ms

call DisplayON_CursorON_BlinkON
Wait_15ms
Wait_4.1ms

call EntryModeSet
Wait_100us

call ClearDisplay
Wait_15ms
Wait_4.1ms

movlw b'01001000' ;H
call SendChar
movlw b'01100101' ;e
call SendChar
movlw b'01101100' ;l
call SendChar
movlw b'01101100' ;l
call SendChar
movlw b'01101111' ;o
call SendChar
movlw b'01010111' ;W
call SendChar
movlw b'01101111' ;o
call SendChar
movlw b'01110010' ;r
call SendChar
movlw b'01101100' ;l
call SendChar
movlw b'01100100' ;d
call SendChar

Eternal
bcf PORTB, 0
nop
bsf PORTB, 0
goto Eternal

;-----------
StrobeData
nop
bsf ENABLE
nop
movwf DATA_PORT
nop
bcf ENABLE
return
;-----------
EntryModeSet
btfsc BUSY_FLAG
goto EntryModeSet
bcf RS
bcf RW
movlw b'00000110'
call StrobeData
return
;-----------
SendChar
btfsc BUSY_FLAG
goto SendChar
bsf RS
bcf RW
call StrobeData
return
;-----------
ClearDisplay
btfsc BUSY_FLAG
goto ClearDisplay
bcf RS
bcf RW
movlw 0x01
call StrobeData
return
;-----------
HomeCursor
btfsc BUSY_FLAG
goto HomeCursor
bcf RS
bcf RW
movlw 0x02
call StrobeData
return
;-----------
DisplayOFF_CursorOFF_BlinkOFF
btfsc BUSY_FLAG
goto DisplayOFF_CursorOFF_BlinkOFF
bcf RS
bcf RW
movlw b'00001000'
call StrobeData
return
;-----------
DisplayOFF_CursorOFF_BlinkON
btfsc BUSY_FLAG
goto DisplayOFF_CursorOFF_BlinkON
bcf RS
bcf RW
movlw b'00001001'
call StrobeData
return
;-----------
DisplayOFF_CursorON_BlinkOFF
btfsc BUSY_FLAG
goto DisplayOFF_CursorON_BlinkOFF
bcf RS
bcf RW
movlw b'00001010'
call StrobeData
return
;-----------
DisplayOFF_CursorON_BlinkON
btfsc BUSY_FLAG
goto DisplayOFF_CursorON_BlinkON
bcf RS
bcf RW
movlw b'00001011'
call StrobeData
return
;-----------
DisplayON_CursorOFF_BlinkOFF
btfsc BUSY_FLAG
goto DisplayON_CursorOFF_BlinkOFF
bcf RS
bcf RW
movlw b'00001100'
call StrobeData
return
;-----------
DisplayON_CursorOFF_BlinkON
btfsc BUSY_FLAG
goto DisplayON_CursorOFF_BlinkON
bcf RS
bcf RW
movlw b'00001101'
call StrobeData
return
;-----------
DisplayON_CursorON_BlinkOFF
btfsc BUSY_FLAG
goto DisplayON_CursorON_BlinkOFF
bcf RS
bcf RW
movlw b'00001110'
call StrobeData
return
;-----------
DisplayON_CursorON_BlinkON
btfsc BUSY_FLAG
goto DisplayON_CursorON_BlinkON
bcf RS
bcf RW
movlw b'00001111'
call StrobeData
return
;-----------
END
Click to expand...
 
"Will" <larkmore@aol.com> wrote in message
news:5faf6114.0402031434.38db8ce2@posting.google.com...

with 10KOhm pulldown resistors to ground on ALL of the lines on the
Click to expand...
I think one pin on the most PICs is open collector.
 
"Meindert Sprang" <mhsprang@NOcustomSPAMware.nl> wrote in message news:<40209d2c$1@news.nb.nu>...
Your strobedata routine is too fast. Many LCD displays have a cycle time of
500ns to 1000ns, where the E has to be kept high for 300 to 500ns or longer.
Click to expand...
I'm not sure how you're arriving at that conclusion. The formula I
used to determine how long the enable pin strobed was as follows:
For a PIC
20 MHz external resonator/crystal -> 5MHz instruction rate (clock/4)
-> 200 ns per instruction.

Even assuming worst case that the PIC sets the pin high at the very
end of the BSF instruction and low at the very beginning of the BCF
instruction, there are 3 instructions between them. At 200ns each,
that's at least 600ns and possibly 800ns if everything lines up
nicely. I've also checked it with a scope probe and it looks more
than long enough. In fact, I have verified that the PIC is in fact
sending the signals I thinnk it should be at the right timing, based
upon the datasheet that Optrex had on their website. In case anyone
cares, that file was
Dmcman_full.pdf and had 58 pages. It had no revisions listed on the
second page so I guess it was revision 0.
 
Will wrote:
I have an Optrex LCD (DMC-20481NY-LY-AGE) that is 4x20 characters and
driven by a Microchip PIC16F877 running at 20MHz. I know I got this
exact same physical LCD to work before but for the life of me I can't
recall what trick I used to do so. Attached at the end is my
software. I get power to the LCD, but all I see is lines 1 and 3 as
all dark and lines 2 and 4 as all clear. Hunting around newsgroups
leads me to think my initialization routines aren't working (gee, ya
think?!?!) but as near as I can tell I have met or exceeded all of the
timing requirements for data transfer. PLEASE HELP!!!!! If it
matters, I am using a dedicated 5V DC supply to drive both the PIC and
the LCD. The PIC is connected to the LCD through 330 Ohm resistors,
with 10KOhm pulldown resistors to ground on ALL of the lines on the
PIC side. This was because I was seeing a lot of glitches on powerup
due to ports being inputs. Each line also has a .01uF cap to ground
and there is a bypass capacitor on the 5V line to ground next to the
PIC. The BusyFlag is also connected directly from the LCD to the PIC
on PORTB, 6. Thanks for any insight!
-Will
Click to expand...

(Maybe it's obvious from your code .... but I didn't read it.)
The first thing I'd do is get rid of all the pulldowns and caps; you can
add 'em all later if you really-really have to. I've driven half a
dozen different LCDs with three kinds of PICs for several years and
never needed all that extra hardware.

The most persistant bug in my LCD boilerplate setup routines is that
it's 5x8 dots, 2x20 display and the LCD I've got hooked up is different
from those. I recall being in the same boat as you are now ... for
days! ... gnashing my teeth because I _knew_ the code worked (I was
looking at at earlier project that used the same code), and I _knew_ the
LCD was OK (because it worked when hooked up to a different project).
Yes, it was a case of operator error; the display that wouldn't
initialize was not a 2x20 but a 1x16.
 
CWatters wrote:
"Will" <larkmore@aol.com> wrote in message
news:5faf6114.0402031434.38db8ce2@posting.google.com...

with 10KOhm pulldown resistors to ground on ALL of the lines on the

I think one pin on the most PICs is open collector.
Click to expand...

Ah yes ... the famous open collector gotcha. That's another trap for
amateurs. It still bites me from time to time, even after upteen
Microchip projects.
 
"Will" <larkmore@aol.com> wrote in message
news:5faf6114.0402040514.57b699fd@posting.google.com...
"Meindert Sprang" <mhsprang@NOcustomSPAMware.nl> wrote in message
news:<40209d2c$1@news.nb.nu>...
Your strobedata routine is too fast. Many LCD displays have a cycle time
of
500ns to 1000ns, where the E has to be kept high for 300 to 500ns or
longer.

I'm not sure how you're arriving at that conclusion.
Click to expand...
By reading the datasheets and experience. Driving earlier LCD's from a '51
bus was already a problem. You had to use nifty adressing tricks to get it
running as a memory mapped device. the other solution was to drive the port
pins directly.

But I strongly suggest to remove the caps. Your signals do not have the
proper rise and fall time requirements. And they simply block a strobe as as
short as a microsecond.

Meindert
 
Ok, I've had limited success so far. Circuit-wise I have removed the
capacitors from the data lines but left the series and pulldown
resisitors alone. Program-wise I have added enourmous delays to the
initialization routines and reordered some of the commands. The
combination seems to have done the trick for initializing the display
since I now get a blinking cursor and some letters. I say some
letters, because there is still a timing glitch I can't seem to track
down. I know it has to do with trying to use the Busy Flag instead of
hard coded delays, but despite searching the web and pouring over
cryptic datasheets I cannot find a solution that works. If someone
familiar with PIC assembly could post a WORKING snippet of code for a
20MHz crystal, or if someone could just post a graphical plot of
signals versus time for checking the busy flag I would greatly
appreciate it! My new code is appended below. Thanks for all the
help!
-Will

; LCD Control Software
;
; Software uses a 20MHz crystal
; for timing.
;

;******************************************************************
Stall MACRO
LOCAL Stall_Jump
goto Stall_Jump
Stall_Jump
ENDM
;******************************************************************
Wait_15ms MACRO
LOCAL OuterLoop
LOCAL InnerLoop

movlw .59
movwf OUTER_COUNTER
OuterLoop
movlw .255
movwf INNER_COUNTER
InnerLoop
Stall
decfsz INNER_COUNTER, F
goto InnerLoop
decfsz OUTER_COUNTER, F
goto OuterLoop
ENDM
;******************************************************************
Wait_4.1ms MACRO
LOCAL OuterLoop
LOCAL InnerLoop

movlw .17
movwf OUTER_COUNTER
OuterLoop
movlw .255
movwf INNER_COUNTER
InnerLoop
Stall
decfsz INNER_COUNTER, F
goto InnerLoop
decfsz OUTER_COUNTER, F
goto OuterLoop
ENDM
;******************************************************************
Wait_100us MACRO
LOCAL InnerLoop

movlw .100
movwf INNER_COUNTER
InnerLoop
Stall
decfsz INNER_COUNTER, F
goto InnerLoop
ENDM
;******************************************************************
CheckBusyFlag MACRO
LOCAL JumpPoint
JumpPoint
bcf RS
bsf RW
nop
nop
bsf ENABLE
nop
nop
nop
nop
nop
bcf ENABLE
btfsc BUSY_FLAG
goto JumpPoint
ENDM
;******************************************************************
list p=16F877

; Include file, change directory if needed
include "p16f877.inc"

#define ENABLE PORTE, 2
#define RS PORTE, 1
#define RW PORTE, 0

#define DATA_PORT PORTD
#define BUSY_FLAG PORTB, 6

OUTER_COUNTER equ 0x20
INNER_COUNTER equ 0x21

W_TEMP equ 0x70
STATUS_TEMP equ 0x71
PCLATH_TEMP equ 0x72


;//Reset Vector
Org 0x00
clrf PCLATH ; ensure page bits are cleared
goto Initialize

;//Interrupt Vector
ORG 0x04
MOVWF W_TEMP ;Copy W to TEMP register
SWAPF STATUS,W ;Swap status to be saved into W
CLRF STATUS ;bank 0, regardless of current bank, Clears
IRP,RP1,RP0
MOVWF STATUS_TEMP ;Save status to bank zero STATUS_TEMP
register
MOVF PCLATH, W ;Only required if using pages 1, 2 and/or 3
MOVWF PCLATH_TEMP ;Save PCLATH into W
CLRF PCLATH ;Page zero, regardless of current page

;TO DO: Fill in for interrupt vectoring

banksel PCLATH_TEMP
MOVF PCLATH_TEMP, W ;Restore PCLATH
MOVWF PCLATH ;Move W into PCLATH
SWAPF STATUS_TEMP,W ;Swap STATUS_TEMP register into W
;(sets bank to original state)
MOVWF STATUS ;Move W into STATUS register
SWAPF W_TEMP,F ;Swap W_TEMP
SWAPF W_TEMP,W ;Swap W_TEMP into W
retfie ; return from interrupt

;//Initialization from powerup
Initialize
clrf INTCON
clrf INTCON
CGIE
bcf INTCON, GIE
btfsc INTCON, GIE
goto CGIE
clrf INTCON

; //Declare port/pin definitions
banksel TRISA
movlw B'00000111'
movwf ADCON1 ; Port A is all digital
movlw B'00000000'
movwf TRISA ; Port A is OOOOOOOO
movlw B'01000000'
movwf TRISB ; Port B is OIOOOOOO
movlw B'10000001'
movwf TRISC ; Port C is IOOOOOOI
movlw B'00000000'
movwf TRISD ; Port D is OOOOOOOO
bcf TRISE, PSPMODE ; Turn off the parallel port
bcf TRISE, 0 ; Port E is -----OOO
bcf TRISE, 1
bcf TRISE, 2
bsf OPTION_REG, 7 ;Turn off port B pullups

banksel PORTB
call Big_Delay
call Big_Delay
call Big_Delay
call Big_Delay

banksel OUTER_COUNTER
bsf PORTB, 7

Wait_15ms
Wait_15ms

bcf PORTB, 7

bcf RS
bcf RW
movlw b'00111000'
call StrobeData

Wait_15ms
Wait_15ms

bcf RS
bcf RW
movlw b'00111000'
call StrobeData

Wait_15ms
Wait_15ms

bcf RS
bcf RW
movlw b'00111000'
call StrobeData

Wait_15ms
Wait_15ms

bcf RS
bcf RW
movlw b'00111000'
call StrobeData

Wait_15ms
Wait_15ms

call DisplayOFF_CursorOFF_BlinkOFF
Wait_15ms
Wait_15ms

call ClearDisplay
Wait_15ms
Wait_15ms

call EntryModeSet
Wait_15ms
Wait_15ms

call DisplayON_CursorON_BlinkON
Wait_15ms
Wait_15ms

movlw b'01001000' ;H
call SendChar
movlw b'01100101' ;e
call SendChar
movlw b'01101100' ;l
call SendChar
movlw b'01101100' ;l
call SendChar
movlw b'01101111' ;o
call SendChar
movlw b'01010111' ;W
call SendChar
movlw b'01101111' ;o
call SendChar
movlw b'01110010' ;r
call SendChar
movlw b'01101100' ;l
call SendChar
movlw b'01100100' ;d
call SendChar

Eternal
bsf PORTB, 0
nop
bcf PORTB, 0
goto Eternal

;-----------
StrobeData
nop
bsf ENABLE
nop
nop
movwf DATA_PORT
nop
nop
bcf ENABLE
return
;-----------
EntryModeSet
CheckBusyFlag
bcf RW
movlw b'00000110'
call StrobeData
return
;-----------
SendChar
CheckBusyFlag
bsf RS
bcf RW
call StrobeData
return
;-----------
ClearDisplay
CheckBusyFlag
bcf RW
movlw 0x01
call StrobeData
return
;-----------
HomeCursor
CheckBusyFlag
bcf RW
movlw 0x02
call StrobeData
return
;-----------
DisplayOFF_CursorOFF_BlinkOFF
CheckBusyFlag
bcf RW
movlw b'00001000'
call StrobeData
return
;-----------
DisplayOFF_CursorOFF_BlinkON
CheckBusyFlag
bcf RW
movlw b'00001001'
call StrobeData
return
;-----------
DisplayOFF_CursorON_BlinkOFF
CheckBusyFlag
bcf RW
movlw b'00001010'
call StrobeData
return
;-----------
DisplayOFF_CursorON_BlinkON
CheckBusyFlag
bcf RW
movlw b'00001011'
call StrobeData
return
;-----------
DisplayON_CursorOFF_BlinkOFF
CheckBusyFlag
bcf RW
movlw b'00001100'
call StrobeData
return
;-----------
DisplayON_CursorOFF_BlinkON
CheckBusyFlag
bcf RW
movlw b'00001101'
call StrobeData
return
;-----------
DisplayON_CursorON_BlinkOFF
CheckBusyFlag
bcf RW
movlw b'00001110'
call StrobeData
return
;-----------
DisplayON_CursorON_BlinkON
CheckBusyFlag
bcf RW
movlw b'00001111'
call StrobeData
return
;-----------
ShiftCursorRight
CheckBusyFlag
bcf RW
movlw b'00010100'
call StrobeData
return
;-----------
ShiftCursorLeft
CheckBusyFlag
bcf RW
movlw b'00010000'
call StrobeData
return
;-----------
ShiftDisplayRight
CheckBusyFlag
bcf RW
movlw b'00011100'
call StrobeData
return
;-----------
ShiftDisplayLeft
CheckBusyFlag
bcf RW
movlw b'00011000'
call StrobeData
return
;-----------
;******************************************************************
Little_Delay
Stall
Stall
Stall
Stall
Stall
Stall
Stall
Stall
Stall
Stall
Stall
Stall
Stall
Stall
Stall
Stall
Stall
Stall
Stall
Stall
Stall
Stall
Stall
Stall
Stall
Stall
Stall
Stall
Stall
Stall
Stall
Stall
Stall
Stall
Stall
Stall
Stall
Stall
Stall
Stall
Stall
Stall
Stall
Stall
Stall
Stall
Stall
Stall
Stall
Stall
Stall
Stall
Stall
Stall
Stall
Stall
Stall
Stall
Stall
Stall
Stall
Stall
Stall
Stall
Stall
Stall
Stall
Stall
Stall
Stall
return
Big_Delay
call Little_Delay
call Little_Delay
call Little_Delay
call Little_Delay
call Little_Delay
call Little_Delay
call Little_Delay
call Little_Delay
call Little_Delay
call Little_Delay
call Little_Delay
call Little_Delay
Medium_Delay
call Little_Delay
call Little_Delay
call Little_Delay
call Little_Delay
call Little_Delay
call Little_Delay
call Little_Delay
call Little_Delay
call Little_Delay
call Little_Delay
call Little_Delay
call Little_Delay
call Little_Delay
return
;-----------
END
 
On Wed, 4 Feb 2004 10:52:04 PST, Everett M. Greene wrote:

larkmore@aol.com (Will) writes:
I have an Optrex LCD (DMC-20481NY-LY-AGE) that is 4x20 characters and
driven by a Microchip PIC16F877 running at 20MHz. I know I got this
exact same physical LCD to work before but for the life of me I can't
recall what trick I used to do so. Attached at the end is my
software. I get power to the LCD, but all I see is lines 1 and 3 as
all dark and lines 2 and 4 as all clear. Hunting around newsgroups
leads me to think my initialization routines aren't working (gee, ya
think?!?!) but as near as I can tell I have met or exceeded all of the
timing requirements for data transfer. PLEASE HELP!!!!! If it
matters, I am using a dedicated 5V DC supply to drive both the PIC and
the LCD. The PIC is connected to the LCD through 330 Ohm resistors,
with 10KOhm pulldown resistors to ground on ALL of the lines on the
PIC side. This was because I was seeing a lot of glitches on powerup
due to ports being inputs. Each line also has a .01uF cap to ground
and there is a bypass capacitor on the 5V line to ground next to the
PIC. The BusyFlag is also connected directly from the LCD to the PIC
on PORTB, 6. Thanks for any insight!

No comment on the hardware aspect of your design, but
putting caps on data lines is unusual to say the least.

The main problem with getting Optrex LCDs to work is the
initialization. The info provided by Optrex is only
approximately accurate with respect to the time delays.
I've had to insert looooong delays at each initialization
step and then shorten them until failure, thus finding
that some had to be substantially longer than Optrex
says.

I had exactly the same experience - took many frustrating hours to figure
Click to expand...
out and Optrex was zero help.

There's also a gotcha with the BUSY flag -- it doesn't
start working at the point in the initialization
process that Optrex states. A wait loop has to be
used at each step until the end of initialization.
The BUSY flag can and should be used from there onward.
Click to expand...
Yup
 
Will wrote:
Ok, I've had limited success so far. Circuit-wise I have removed the
capacitors from the data lines but left the series and pulldown
resisitors alone. Program-wise I have added enourmous delays to the
initialization routines and reordered some of the commands. The
combination seems to have done the trick for initializing the display
since I now get a blinking cursor and some letters. I say some
letters, because there is still a timing glitch I can't seem to track
down. I know it has to do with trying to use the Busy Flag instead of
hard coded delays, but despite searching the web and pouring over
cryptic datasheets I cannot find a solution that works. If someone
familiar with PIC assembly could post a WORKING snippet of code for a
20MHz crystal, or if someone could just post a graphical plot of
signals versus time for checking the busy flag I would greatly
appreciate it! My new code is appended below. Thanks for all the
help!
Click to expand...
I seem to remember that you were saying the Busy flag was connected to
bit 6 Port B. Odd, because the busy flag is the highest data bit (bit 7)
if I remember this right. Can you check your busy flag definition
against the data sheet of the LCD chip? Have you got the data sheet of
the HD44780, which is the prototypical chip everyone emulates?

CheckBusyFlag MACRO
LOCAL JumpPoint
JumpPoint
bcf RS
bsf RW
nop
nop
bsf ENABLE
nop
nop
nop
nop
nop
bcf ENABLE
btfsc BUSY_FLAG
goto JumpPoint
ENDM
Click to expand...
I consider it advisable to change the order of the bcf and btfsc
instructions, because the former disables the output of the data that
you are reading with the second.

--
Cheers
Stefan
 
larkmore@aol.com (Will) writes:
I have an Optrex LCD (DMC-20481NY-LY-AGE) that is 4x20 characters and
driven by a Microchip PIC16F877 running at 20MHz. I know I got this
exact same physical LCD to work before but for the life of me I can't
recall what trick I used to do so. Attached at the end is my
software. I get power to the LCD, but all I see is lines 1 and 3 as
all dark and lines 2 and 4 as all clear. Hunting around newsgroups
leads me to think my initialization routines aren't working (gee, ya
think?!?!) but as near as I can tell I have met or exceeded all of the
timing requirements for data transfer. PLEASE HELP!!!!! If it
matters, I am using a dedicated 5V DC supply to drive both the PIC and
the LCD. The PIC is connected to the LCD through 330 Ohm resistors,
with 10KOhm pulldown resistors to ground on ALL of the lines on the
PIC side. This was because I was seeing a lot of glitches on powerup
due to ports being inputs. Each line also has a .01uF cap to ground
and there is a bypass capacitor on the 5V line to ground next to the
PIC. The BusyFlag is also connected directly from the LCD to the PIC
on PORTB, 6. Thanks for any insight!
Click to expand...
No comment on the hardware aspect of your design, but
putting caps on data lines is unusual to say the least.

The main problem with getting Optrex LCDs to work is the
initialization. The info provided by Optrex is only
approximately accurate with respect to the time delays.
I've had to insert looooong delays at each initialization
step and then shorten them until failure, thus finding
that some had to be substantially longer than Optrex
says.

There's also a gotcha with the BUSY flag -- it doesn't
start working at the point in the initialization
process that Optrex states. A wait loop has to be
used at each step until the end of initialization.
The BUSY flag can and should be used from there onward.
 
Make sure you give the LCD time to power up. I just hooked
up a Optrex 2x16 display to a TI MSP430 and I had to put in huge
delays before I ever started initializing the LCD. After I did
that all of my problems went away....

--
Greg Deuerling
Fermi National Accelerator Laboratory
P.O.Box 500 MS368 Batavia, IL 60510
(630)840-4629 FAX (630)840-5406
Electronic Systems Engineering Group
Work: egads_AT_fnal.gov, remove '_AT_'
 
On Wed, 04 Feb 2004 14:21:52 GMT, NoSpam@att.net said...
CWatters wrote:

"Will" <larkmore@aol.com> wrote in message
news:5faf6114.0402031434.38db8ce2@posting.google.com...

with 10KOhm pulldown resistors to ground on ALL of the lines on the

I think one pin on the most PICs is open collector.


Ah yes ... the famous open collector gotcha. That's another trap for
amateurs. It still bites me from time to time, even after upteen
Microchip projects.
Click to expand...
/MCLR is OC when used as a data line - isn't that one of 'em? Works
as an out only, IIRC.
--
Best Regards,
Mike
 
On 3 Feb 2004 14:34:31 -0800, larkmore@aol.com said...
I have an Optrex LCD (DMC-20481NY-LY-AGE) that is 4x20 characters and
driven by a Microchip PIC16F877 running at 20MHz.
Click to expand...
<snip>

I haven't used Optrex yet but My biggest prob getting those black
lines to go away and everything else to init was that I left the
R/W line open. The controller inputs have internal weak pullups so
you have to either tie R/W low or drive it with the PIC.

The other thing I found was that the home command was pretty
useless or something like that. It didn't do what the HDwhatever
Spec sheet said. I have to use Clear Display.

Also, resetting the PIC which runs my LCD init code sometimes
doesn't give the LCD enough time to do whatever it needs to do, I
have to power down the LCD.

I'm not sure, but for the 4 bit interface, I may have had to run
the init code twice. Once to get it in 4 bit mode and again once
it's there.

--
Best Regards,
Mike
 
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