Memory map

[Gary C]

Hi

I have a ZX81 issue 1 with the 622 ROM and the classic MEMOPAK 16K and I think I have a problem with the memory (3d monster maze wont run !)

When I hackup a memory test, locations from 32725 to 32768 seem to be faulty.

But I can't find a straight forward memory map to check if this area is being used for anything or if its actually a problem.

I could just whip out all the RAM's and put them in the tester, but its a bit of a pain and risks damage.

Does anyone have a link to the definitive memory map(s) ?

[1024MAK]

Does this topic help?

Mark

[Paul]

From 32768 downwards is the Z80 stack that's definitely used once the Z80 runs

[1024MAK]

ZX81 16K RAM Memory Test Program

Hi, can you try this test program.

First from the command line enter directly these commands:

POKE 16388,0
POKE 16389,68
NEW

This sets RAMTOP to 17408

Then enter and run this program

Code: Select all

5 FAST
10 LET A=17408
15 LET A=A+1024
20 IF A>32767 THEN GOTO 80
25 PRINT
30 LET B=PEEK A
35 POKE A,0
40 LET C=PEEK A
45 POKE A,170
50 LET D=PEEK A
55 POKE A,85
60 LET E=PEEK A
65 PRINT A;",";B;",";C;",";D;",";E;" ";
70 IF C=0 AND D=170 AND E=85 THEN GOTO 15
75 PRINT "ERROR"
80 PRINT "END"
85 SLOW

This is the result on one of my ZX81's with a Memotech 16k RAM pack:


In terms of the actual system use of the memory, have a look at this document and Chapter 27 of the Sinclair ZX81 BASIC Programming by Steven Vickers (Second Edition 1981)

Mark

[Gary C]

From 32768 downwards is the Z80 stack that's definitely used once the Z80 runs

Ah, the stack is up there ?

Thats why I'm seeing changing numbers.

Ran a test of memory from 18000, up to 32768 and it was only the last few bytes that didn't play so the memory is probably ok.

But it looks like a good idea to lower RAMTOP and do it again just to make sure.

Wonder why 3d maze wont work.