Pair of MC9S08AC60-cannot program-periodic reset?

[mfugere]

Hello,

I am migrating a design from using a pair of older MC908GP32 microcontrollers to a pair of MC9S08AC60CPUE devices.  I am using P&E Micro USB Universal MultiLink and CodeWarrior Special Edition 10.6 in Win7 or the Classic IDE version on XP.  In the original design with the MON08-based MC908GP32 units, the /RST pins were tied together on the controllers - presumably so a fault reset on one would induce a reset on the other.   Each device was programmable with P&E Micro's MON08 version Multilink cable. It all worked fine.

In the new design, I kept both /RESET pins on the MC9S08AC60 microcontrollers tied together, and brought the net trace also out to the RESET pins on the separate 6-pin BKGND debug headers (1 header for each device), but all tied to a common /RESET net.

I cannot program either device because it seems I cannot stay in BKGND mode. Always end up with Error 34 from PE Micro/programmer interface.  Vcc is very stable (5.0V), and there are 0.1uF caps on the RESET pins on each device. Placing a scope probe on the RESET pins indicates one (or both) of the new devices causing /RESET to pulse low approximately 75 milliseconds apart before going high again, even with new programming cable attached.  Is this normal behavior for brand new (virgin) devices?    If so, I guess I need to separate the /RESET pin connections to each micro and its respective  BKGD programming header so they don't interfere?

Thanks for any advice!

Mike

[mfugere]

Yes, indeed - having the RESET lines tied together - which was OK for the MC908GP processors that used the MON08 ROM routines, doesn't work well with the BKGND Debug controllers in the MC9S08AC60 devices.   Separating the (2) /RESET lines allows the Universal MultiLink programmer to do its job and unprotect, erase, and program the chips.

I will have to look at wiring and output pin to an IRQ pins on the devices to see about implementing a method to allow each device to cause a reset-inducing interrupt on the other.

I'll leave this here for posterity/future reference.