This is strange, I hooked up 3.3v GND then TX and PPS from the board to my FPGA kit, I started getting PPS and TX bitstream and I was thrilled. Red light came on, started to blink when it locked.
Went out, came back and picked up where I left off. Turn on everything and Red Light on venus was dim red?? I cut the wires I just soldered in and then realized I can only make the venus work if I connect the outputs TX and PPS after the power. What have I missed?
a dim led may mean a bad startup, which will occour if you have a dry solder joint on the capacitor and resistor on pin 1 or capacitors on the pin 2 of the IC. try wetting them with solder once, may be it helps. doesnt seem that you are doing any thing wrong
I found I can permanently connect the TX pin, connect PPS after power-up and start properly, I will work on my UART segment then worry about the PPS. Still a bit bizarre I have to power-up then connect PPS, I will resolder the PPS wire.
Have you tried using a resistor to connect the PPS to your FPGA?
GM, thats a good idea, when I get home I will try that
I’ve got the same issue when I wired up the PPS pin. I can confirm the resistor does work, it needs to be high resistance. I’m using 1M ohm reliably.
Most likely what is happening is that the GPS module is being parasitically powered via the PPS pin which usually wreaks havoc with proper operation of electronic circuits. When I power a subsystem down (like the GPS module) I will drive any pins connected to it to a logic low.
HTH,
gm