sychronize outside signal

[Arron]

In my project, the main clock is 10MHz and the input signal is a 1kHz
square wave. I hope to detect the rising edge of the input signal and
output a high level voltage for one clock when it were detected. I use
finite state machine to realize the design in Altera Quartus II, the
simulation is OK. But the hardware (Cyclone) gives unexpected results:
no output or several clock signals after the rising edge of input
signal. Does anybody know other method to my project? Thank you in
advance.

 

[Mark]

Are you using a re-synchronizer (two or more back to back flip flops)
on the incoming signal or merely sending it straight into the state
machine as an input?

It sounds as though your circuit could be suffering from
metastability.

http://klabs.org/richcontent/General_Application_Notes/mestablestates/xilinx_metastable_recovery.pdf

Try re-synchronising the signal first. The remaining logic for a
rising ede detect is then trivial.

jianju.ee@polyu.edu.hk (Arron) wrote in message news:<4192d666.176411062@news.polyu.edu.hk>...

In my project, the main clock is 10MHz and the input signal is a 1kHz
square wave. I hope to detect the rising edge of the input signal and
output a high level voltage for one clock when it were detected. I use
finite state machine to realize the design in Altera Quartus II, the
simulation is OK. But the hardware (Cyclone) gives unexpected results:
no output or several clock signals after the rising edge of input
signal. Does anybody know other method to my project? Thank you in
advance.

 

[ALuPin]

jianju.ee@polyu.edu.hk (Arron) wrote in message news:<4192d666.176411062@news.polyu.edu.hk>...

In my project, the main clock is 10MHz and the input signal is a 1kHz
square wave. I hope to detect the rising edge of the input signal and
output a high level voltage for one clock when it were detected. I use
finite state machine to realize the design in Altera Quartus II, the
simulation is OK. But the hardware (Cyclone) gives unexpected results:
no output or several clock signals after the rising edge of input
signal. Does anybody know other method to my project? Thank you in
advance.

Hi,

can you give some essential parts of your code to see what
could go wrong?

Rgds
André

 

[Niv]

"Arron" <jianju.ee@polyu.edu.hk> wrote in message
news:4192d666.176411062@news.polyu.edu.hk...

In my project, the main clock is 10MHz and the input signal is a 1kHz
square wave. I hope to detect the rising edge of the input signal and
output a high level voltage for one clock when it were detected. I use
finite state machine to realize the design in Altera Quartus II, the
simulation is OK. But the hardware (Cyclone) gives unexpected results:
no output or several clock signals after the rising edge of input
signal. Does anybody know other method to my project? Thank you in
advance.

As already stated, you may have metastability issues.
Try this:

SIGNAL reg1: STD_LOGIC;
SIGNAL reg2: STD_LOGIC;
SIGNAL reg3: STD_LOGIC;

sync_1khz: PROCESS (reset_n, clk_1mhz)
BEGIN
IF reset_n = '0' THEN
reg1 <= '0';
reg2 <= '0';
ELSIF rising_edge(clk_1mhz) THEN

-- Insert metastability regs;

reg1 <= in_1khz;
reg2 <= reg1;
reg3 <= reg2;

-- Now detect the edge.

IF reg2 = '1' AND reg3 = '0' THEN -- This is the 1KHz rising edge,
delayed by a few 1MHz clock cycles.

-- Do whatever with edge.

END IF;
END IF;

END PROCESS sync_1khz;