Hi all,
I'm writing a simple program to test my ram memory of the my z80 small computer. I write this assembly code:

Code:


On 02H IO address I have connected a simple LED display.
But when I run this program the display show 7EH that is the opcode of the instruction: LD A,(HL) instead of 04H.
Why this???


Code:


please let me know.

thanks rohs

That's rather strange, could you inform us of how this is hooked up (or if it's not a custom hookup, but rather part of a commercial computer, could you give us the name/model)? I assume you're writing to that RAM address to make sure that RAM is hooked up correctly? I am far from being able to help a lot in this situation, but I can suggest for you to tell how you hooked up your RAM module here so someone more experienced can help with more given information.

My guess is that you somehow got the address lines between the Z80 and RAM swapped. The LD A,(HL) instruction is at 0005 and HL is 5000, so perhaps the top nibble is being used as the lower nibble. We would need more information about how the RAM is connected, such as a schematic and picture of your circuit, before we can provide more help.