Background Debug Mode - interface problem

[AJU]

Hello!

I want to read/write eeprom area via BDM mode. Main problem is with connection

I didn't receive any answer from processor. I'm waiting for 150cycles ect ect... but I didn't reiceve any data.

Can you look on attached file, and write me suggestions?

Perhaps is problem with reset time? I don'f find any documentation with detailed explanation of DBM.

Test traget is MC9S12DB128 @ 4MHz clock.

Best regards!

[kef · Accepted solution]

Host initiates every bit transfer, not only writes, but also reads. Slave MCU can't pulse BKGD pin the same like you pulse it. To read bits you should drive BKGD low and release BKGD pin, allowing MCU to keep BKGD low for additional "0" or "1" - time. Then you sample BKGD pin state in the middle of expected "0" and "1" - rising edges. It's normal MCU "didn't answer" read byte command.

The only response MCU is pulsing low and high is SYNC pulse, which allows you to measure MCU speed.

[AJU]

Hello!

Thank You, Kef, for help. Your suggestions was really useful, so now all working ok.

Best Regards!