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No output from serial port on Putty

No output from serial port on Putty

(OP)
I need to control the boot process on an embedded device, so I connected serial console port pins to Putty client, but can't get any output from serial port. I use FTDI TTL-232R-RPi (USB to TTL RS232) cable. I've measured signals on serial console pins, there is -3.15V on RX pin and 0.15V on TX pin. Serial connection settings are correct, COM3, 115200, data bits 8, stop bits 1, parity: none, flow control: none. I used this FTDI cable in the past with another modem, and it worked. What can be the problem?

RE: No output from serial port on Putty

Your SW is pointed at a different Comm Port.
Your FTDI chip is not genuine, and the FTDI Driver is unhappy.
Something is broken.
You're on the wrong pins (not likely, but it happens).
Any number of other possibilities.

RE: No output from serial port on Putty

Jumper pins 2 and 3 on the end of the serial cable and see if what you type in Putty is echoed back to your screen. If it echoes back, you are in good shape, you probably just have the wrong connection settings or you need to swap pins 2/3 (null modem adapter). If it does not echo back, see VE1BLL's comment.

RE: No output from serial port on Putty

(OP)

Quote (JG2828)

Jumper pins 2 and 3 on the end of the serial cable and see if what you type in Putty is echoed back to your screen. If it echoes back, you are in good shape, you probably just have the wrong connection settings or you need to swap pins 2/3 (null modem adapter). If it does not echo back, see VE1BLL's comment.

I jumper pins TX and RX on the end of serial cable and tried type in Putty, it is echoed back correctly. So this show that FTDI cable is OK.
I think I already tried to swap TX and RX pins.

RE: No output from serial port on Putty

(OP)
As I noted, there is signal voltage on Rx pin(-3.15V) and Tx pin(0.15V): does it mean that firmware has access to that console port?

RE: No output from serial port on Putty

Do you have a scope? You keep mentioning Tx pin(0.15V) which is a useless voltage. Does it ever go to some useful voltage? RS232 is supposed to be +/-15V. Over the years with lame laptops the spec has been eroded to allow down to +/-3V. Does it show even that?

Keith Cress
kcress - http://www.flaminsystems.com

RE: No output from serial port on Putty

(OP)
Unfortunately, I have no scope.

RE: No output from serial port on Putty

Look for 'movement' (signal, changing), not steady DC voltages.

If the 2-3 loopback works when connected, and doesn't when not (to distinguish internal loop back), then it's probably working.

So turn your attention to the other end, the embedded device. Perhaps it's not configured to receive.

Debugging serial ports... ...just like the good old days. smile

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