Laptop connected to Null modem cable connected to Nothing: Putty shows nothing
Laptop connected to Null modem cable bridged Tx/Rx pins: Putty shows proper echo
Laptop connected to Null modem cable unbridged connected to Tx/Rx pins on Max232: Putty at 1200 echos keypresses
Sign doesn't respond to anything on the keyboard, no status messages on boot. The sign doesn't send any messages, I'm only getting the signals back that I'm sending. Is it possible that the serial port has been disabled somehow?
".. Laptop connected to Null modem cable unbridged connected to Tx/Rx pins on Max232: Putty at 1200 echos keypresses.."
This would indicate either:
1/ the the board is echoing your keypresses back to your computer
- Kool 'cos this means the board is swallowing serial data and sending it back...
- Confirm this by checking that it ONLY works at 1200 baud
- If so, play with the databits, stop bits and parity settings to see if the response changes.
Only ONE configuration of Baud Rate, databits, stop bits and parity settings should work correctly
Then write a simple program to send all ascii characters to the board.
One after another followed by CR, or LF or CR+LF
and log the values echoed by the board
0X0 0xD & log response
0X0 0xA & log response
0X0 0xD 0xA & log response
0X1 0xD & log response
0X10xA & log response
0X1 0xD 0xA & log response
0XFF 0xD & log response
0XFF 0xA & log response
0XFF 0xD 0xA & log response
One of these sequences should get a repsonse (if only "NAK"= board says whaaat???)
The idea here is to try and deduce the protocol expected by the board.
Many serial protocols expect each packet to always start with a special character
It is also possible that the serial comms needs to be enabled in some fashion
but then one would not expect the port to echo characters sent...
2/ The Max232 is wired as a "null modem" (unlikely)