Charlie's Red Ant - a ROM instruction that reads throughout memory

[PokeMon]

since as hl is stored after this instruction

A bit of all, H is (re)stored after this instruction.

[olofsen]

Thinking about a "claire.p" that shows a "thumbs up" path in the Live Memory View...

[zsolt]

Hi,

Also,

Code: Select all

L0237:  LD      B,(HL)          ; (7) Note. Harmless Nonsensical Timing weight.

Is exactly it

So the fix should be LD H, (HL)

Why is this the solution? This is same memory reading.
Zsolt

[dr beep]

Hi,

Also,

Code: Select all

L0237:  LD      B,(HL)          ; (7) Note. Harmless Nonsensical Timing weight.

Is exactly it

So the fix should be LD H, (HL)

Why is this the solution? This is same memory reading.
Zsolt

The timing must be the same, but B gets a value that is not allowed.
CP (HL) might work too, but it does effect the Z-flag where LD H,(HL) has no effect on flags but still use 7 tstates in 1 command and 1 byte.

[Andy Rea]

Just for fun....

REDSINC.P

(2.11 KiB) Downloaded 404 times

regards Andy .

[olofsen]

Thanks I think I'll have it running all night on real hardware - it works quite well even with monitor switched off and eyes closed

[Andy Rea]

did i forget to mention it works very well on eightyone V1.7

[zsolt]

The timing must be the same, but B gets a value that is not allowed.

OK, it is time-correct, but does not solve the original "problem":

* Yes, the ZX81 appears to have a pet - a restless red 'ant' (escaped from the classic game?) which relentlessly patrols RAM from the end to the start. It's (most likely) a read instruction in the display routine.

(if it is a real problem)

Andy, what should I see there?

[1024MAK]

Well, it's been in the ROM since 1981...

Mark

[sirmorris]

It's not a problem! It's a pet!