Hi Kai,

Thanks for replying.
This may be a silly question, but what exactly did Jez focus on? Was he implying that I needed pull-downs for the off state? or what?
Jez, if you read this, could you please clarify?

About the bus-contention issue - yeah, I know it's dangerous, and was I to do it again I'd definitely make room for some extra discrete logic in there to avoid the situation. The reason I didn't is that pcb space is very cramped - everything barely fits as it is.

As for the RAM, that was just a silly oversight. What would be the standard way to control the Chip Enable? An AND of the !RD and !WR lines?

The reason for the resistor between the supervisor and the reset line is due to a peculiarity with the 89c51 - for the watchdog to function correctly, there must be at lease a 2k resitance between reset and any external circuitry.

Thanks alot for your help,

George Ricketts