RCM6760 serial D,E,F 9600bps 8N2 ... first byte not generate 2 stop bit

Question

RCM6760 UART bug: serial D E F : 9600bps 8N2
baud rate is ok.
first byte generate ONLY 1 stop bit.
after second byte generate 2 stop bit.

Answer 1

I think I see the error in RS232.LIB that causes this problem.

In spx_starttx(), it isn't checking for the 2-stop-bits flag before loading the byte to send. Later, in spx_isr(), it checks that flag and correctly uses SxLR_OFS instead of SxDR_OFS.

I don't have a system set up where I can test this code, but it *should* work. Just replace everything between .send and .exit in spx_starttx() of RS232.LIB with the following:

Code:

.send:
      _READ_BIT_(SER_BIT_TWOSTOP)
      jr    z, .normal_stop
ioi   ld    (iy+SxLR_OFS), L     ; send with an extra stop bit
      jr    .load_done

.normal_stop:
ioi   ld    (iy+SxDR_OFS), L     ; normal send

.load_done:

.exit:

Please let me know if that works for you.

Comments

Tested and released on GitHub.  https://github.com/digidotcom/DCRabbit_10/commit/c7d6a7ded4a3d78c6d38e77c08a8e55e52c5ed4c

Answer 2

hi tom,

I replace your code as you described...
your code fix the bug...
the serial working 8N2 correctly.

thank you!

Answer 3

Hello, im trying to get rid of the start bit, anyone knows how to?

Comments

Please ask this as a new question in the forum, and include additional background information on what you're trying to accomplish, and what you've already tried.