The 68HC812A4 doesn't do PWM, right?  

The '812A4 may not be advertised as doing PWM, but PWM can be generated on up to seven channels with no CPU overhead.  Here's how to do it: 

Set CH7 to the PWM period and use the channel7 reset function to reset the timer counter

The compare values in 0C0-OC6 will now give a PWM output as desired.

In normal modes, the COPCTL register is designated as "Write-Once".  The firmware bootloader residing in the top 256 bytes of EEPROM is the first thing that gets executed following reset in single-chip mode.  It clears the COPCTL register, so any subsequent write to the COPCTL register by your code will be ignored.  If you have a BDM pod, you can use DBug12 to load in a modified version of the bootloader, which doesn't disable the COP.  Of course, it has to service the COP to prevent a timeout.  (Contact us if you would like a copy of the bootloader source code to modify.) 

In expanded modes, the EEPROM is located at $1000 following reset, so the firmware bootloader goes away (ie. it's not in the vector space).  So the MCU fetches the Reset Vector directly from external memory (ie. Flash) upon reset.  Your program should include a pointer there to the first instruction of your code.  You are free to write to the COPCTL register at the beginning of your program.

1. Plug your BDM ribbon cable into the BDM connector on your 812 board ("the target")
2. Set the target board jumpers/switches to Single Chip Mode (ie. MODA=MODB=0).  The position of the BOOT/RUN switch doesn't matter, since it is only used by the bootloader
3. Supply power to your target board only (not the BDM pod)-- the BDM pod will get the 5V it needs via the ribbon cable
4. Use any terminal program at 9600 baud, with the BDM pod connected to your PC's COM port
5. Type device 812a4

• eebase f000

Loading your program into EEPROM (Single Chip Mode): 

• mm f1 0
• bulk
• baud 1200
• load
Then use the ASCII file transfer feature of your terminal program at 1200 baud to send the s-record file to be programmed