Hi Lawrence, I answer your questions.

1. So I assume you actually can toggle P3.1.
Did you check the pulse width of the signal? this way you'll know the system clock is correct. Make sure the crystal works correctly first.

ANS. I can see the wave form generated by microcontroller at pin 18 & 19, 11.1 Mhz, I am using 11.059 Mhz crystal, I can see the same at PSEN & ALE, 1.84 Mhz, I am sure the crystal is working.


2. When you test the short TX routine. Are there anything connected to the circuit?
I'll disconnect "EVERYTHING" that is not necessary for this test from all ports. Do not "assume", sometimes we "assume" a connection to an "input" pin of other device should not cause problems...AND you guess what!!! .

ANS. I disconnected all components, I am just working with the minimum system.

3. put RETI for all unused interrupt vector- just in case.

ANS. I am just declared in the program the address 0023H, serial interruption. If y like you couls see the program, I think I wrote before, this is simple program that send continously ASCII characaters to buffer.


4. Remember, a simulator is a "SIMULATOR" only.

ANS. Yeah, here we have a proverb, I will try to translate; " It's not same look the girl coming, than talk to her", I hope you undertand, the mean is I know is so different, that's for it at simulator works and in the reality do not works like that.

Thanks, I keep going fighting until this works.

PS While it is unlikely...Are you sure that the CPU and EPROM circuit is connected correcly. Would that be the CPU not reading the right instruction at the right address?