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Program that talks via monitor port in RAM doesn't work right running in flash

Question asked by Paul McKneely on Aug 27, 2012
Latest reply on Aug 28, 2012 by Paul McKneely

I just designed a new board around the MC908GZ60CFUE and am talking through the debug port via a program I wrote and downloaded to RAM. The program turns three LEDs on and off via single key commands. I then altered the program so I can burn it into flash and run it that way. There are only two differences between the programs. The RAM version is loaded to starting location $0580 while the flash version is loaded to flash location $8000 plus I am adding this address to the reset vector at $FFFE. Also I am setting IRQ to Vtst for the RAM version vs. Vdd for the flash version for power on reset. I am using an 8MHz crystal and pin inputs are (PTA0=1,TPA1=0,TPB0=1,PTB1=0,PTB4=1) which makes it configure the monitor to generate a 7200 BAUD rate from the 8MHz clock (not divided by 2) for the debug port. When I power up, the Green LED goes on briefly (biased on by a resistor) then it turns off via initialization code like it is supposed to so I know that code is running. However, I can't talk to the debug port any more. I suspect that the monitor does something to configure the PLL which sets the bus clock frequency that my code is not doing. Can anyone tell me what I am missing?

 

Thanks.

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