MC9S12DP512 SCI Issues

[tnriley]

I have an application using the SCI0 port on the MC9S12DP512 controller. I am using a PE Micro Multilink debugger to load the code and Codewarrior Development studio v5.9.0 build 5294. I am using the SCI port  connected to a MAX3222e chip as a link to an external local PC for poeriodic unit monitoring. The serial port comms work as expected when the unit is running with debugger attached. But, when I detatch debugger I have very unreliable comms over the serial port connection to the local PC. May get 1 response out of 5 tries. Any ideas on how to track down this issue? SCI1:155.2k BAUD comms, 8,N,1 setup.

As a side note, the PLL is working as expected, as measured via the ECLK output, for both cases. SCI0 is connected to an internal MKS transducer and is working fine for both cases. I can tell because the hardware is pressure cycling as expected. I also have an activity LED connected to a PORTA pin that toggles at 1 sec intervals.

[lama · Accepted solution]

Hi,

This type of issue usually leads to the root casue of setting registers which are write once only in a normal mode but anytime in special mode.
I would like to suggest you to either check all possible mistakes related to write once only registers or to create an simplified project with Tx only, no pll, and measure Tx pin whether it has correct behavior and expected baud rate. For second case you'll be sure you do something wrong with the MCU setup.

Best regards,

Ladislav