TTL/RS-232 Conversion circuit interface

[Will]

Hi All,

I am interfacing a ham radio to a computer to program it and I have been
looking at various TTL / RS-232 conversion circuits. However I happen to
have a commercial ADMS programming cable I use with my Yaesu VX-7R radio
(ham radio). This cable also handles this type of conversion so I am
thinking why reinvent the wheel when I can utilize this existing circuit
which is already integrated into the D-sub shell of this cable.

Thus my question:

These generic circuits appear to RS-232 logic levels (+/-12VDC) on pins 2 &
3 of a DB9 connector and converts them to 0 & 5VDC. Which TTL voltage
corresponds to a logic 0 and which to a logic 1? On the RS-232 side, the
data pins use negative logic, so +3 to +12 VDC is logic 0 and -3 to -12VDC
is logic 1. Does the TTL data input use positive logic instead ( logic 1 is
+5VDC and logic 0 is 0VDC)?

What is the industry convention when terminating the TTL side of this cable
to a stereo plug. ... is the tip conductor logic 1 or logic 0? Once I
determine this, then I will use this existing conversion cable and simply
wire the stereo plug conductors to their respective TXD and RXD pins on my
Yaesu FT-857.

Lastly, what happens if one connects the TTL level TX conductor to the TXD
pin on the radio side accidentally instead of the RXD pin on the radio?
i.e. wires crossed in error

Thanks for any and all info!

73's Will

 

[Ryan weihl]

Will wrote:

Hi All,

I am interfacing a ham radio to a computer to program it and I have been
looking at various TTL / RS-232 conversion circuits. However I happen to
have a commercial ADMS programming cable I use with my Yaesu VX-7R radio
(ham radio). This cable also handles this type of conversion so I am
thinking why reinvent the wheel when I can utilize this existing circuit
which is already integrated into the D-sub shell of this cable.

Thus my question:

These generic circuits appear to RS-232 logic levels (+/-12VDC) on pins 2 &
3 of a DB9 connector and converts them to 0 & 5VDC. Which TTL voltage
corresponds to a logic 0 and which to a logic 1? On the RS-232 side, the
data pins use negative logic, so +3 to +12 VDC is logic 0 and -3 to -12VDC
is logic 1. Does the TTL data input use positive logic instead ( logic 1 is
+5VDC and logic 0 is 0VDC)?

on the RS232 side data marking condition is defined as a negative

voltage i.e. mark -3v to -12 = +5V on the TTL side

What is the industry convention when terminating the TTL side of this cable
to a stereo plug. ... is the tip conductor logic 1 or logic 0? Once I
determine this, then I will use this existing conversion cable and simply
wire the stereo plug conductors to their respective TXD and RXD pins on my
Yaesu FT-857.

Lastly, what happens if one connects the TTL level TX conductor to the TXD
pin on the radio side accidentally instead of the RXD pin on the radio?
i.e. wires crossed in error

Thanks for any and all info!

73's Will

 

[Will]

Hi Ryan,

One more related question:

On the RS-232 side, the TXD side is typically held in a mark state (logic 1)
if I recall correctly (hence -3v to -12v) until the next byte for
transmision. If I view the TTL side of this TXD line, should I expect to
see this pin pulled up to 5V?

Essentially, what I would like to do is be able to differentiate between the
TXD and RXD TTL level pins on a dual channel scope to double check my
interface to the radio. Thus, with this conversion cable connected to a
computer with an active Hyperterminal and holding a given keyboard key down.

--Will

These generic circuits appear to RS-232 logic levels (+/-12VDC) on pins
2 &
3 of a DB9 connector and converts them to 0 & 5VDC. Which TTL voltage
corresponds to a logic 0 and which to a logic 1? On the RS-232 side,
the
data pins use negative logic, so +3 to +12 VDC is logic 0 and -3
to -12VDC
is logic 1. Does the TTL data input use positive logic instead ( logic
1 is
+5VDC and logic 0 is 0VDC)?

on the RS232 side data marking condition is defined as a negative
voltage i.e. mark -3v to -12 = +5V on the TTL side

 

[ryan wiehle]

Will wrote:

Hi Ryan,

One more related question:

On the RS-232 side, the TXD side is typically held in a mark state
(logic 1) if I recall correctly (hence -3v to -12v) until the next
byte for transmision. If I view the TTL side of this TXD line,
should I expect to see this pin pulled up to 5V?

yes, on the TTL side mark = +5v, and thats the way the RS232 chips
work. Max or Dallas or whatever

Essentially, what I would like to do is be able to differentiate
between the TXD and RXD TTL level pins on a dual channel scope to
double check my interface to the radio. Thus, with this conversion
cable connected to a computer with an active Hyperterminal and
holding a given keyboard key down.

--Will

These generic circuits appear to RS-232 logic levels (+/-12VDC)
on pins
2 &
3 of a DB9 connector and converts them to 0 & 5VDC. Which TTL
voltage corresponds to a logic 0 and which to a logic 1? On the
RS-232 side,
the
data pins use negative logic, so +3 to +12 VDC is logic 0 and -3
to -12VDC
is logic 1. Does the TTL data input use positive logic instead (
logic
1 is
+5VDC and logic 0 is 0VDC)?

on the RS232 side data marking condition is defined as a negative
voltage i.e. mark -3v to -12 = +5V on the TTL side

TXd and RXd will both be logic 1 in idle mode i.e. +5V on the ttl and
-3 to -12V on the RS232 side