Greetings. Upon finding that the project which I am working on was not functioning as it should, I went through a number of troubleshooting steps. Once I reached the point I couldn't figure it out, I undid everything and started over.

My discovery was that in attempting to work with an external address, the low-byte was not being delt with correctly.

Making a quick and dirty test circuit, I found that the output of the address was not doing as it should. Inspecting individual pins, I noticed that ALE was going insane. Rather than triggering to latch the low byte, it simply oscillates without any obvious cause.

Here is the EXACT code I used for this test:


;----------- initial.
MOV P1, #0x00
MOV A, #0xFF
MOV DPTR, #0x0055
MOVX @DPTR, A

Loop:
JMP Loop

result: A0-7=0xFF ALE: oscillating.

Any ideas of what I'm doing incorrectly?