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

Discussion about ZX80 / ZX81 Software
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PokeMon
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Re: Charlie's Red Ant - a ROM instruction that reads throughout memory

Post by PokeMon » Mon Sep 11, 2017 5:02 pm

Andy Rea wrote:
Sun Sep 10, 2017 9:35 pm
since as hl is stored after this instruction
A bit of all, H is (re)stored after this instruction. :mrgreen:

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

Post by olofsen » Mon Sep 11, 2017 5:23 pm

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

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

Post by zsolt » Tue Sep 12, 2017 3:58 pm

Hi,
dr beep wrote:
Sun Sep 10, 2017 9:22 pm
sirmorris wrote:
Sun Sep 10, 2017 5:59 pm
Also,

Code: Select all

L0237:  LD      B,(HL)          ; (7) Note. Harmless Nonsensical Timing weight.
Is exactly it :D
So the fix should be LD H, (HL)
Why is this the solution? :o This is same memory reading.
Zsolt

dr beep
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Re: Charlie's Red Ant - a ROM instruction that reads throughout memory

Post by dr beep » Tue Sep 12, 2017 5:25 pm

zsolt wrote:
Tue Sep 12, 2017 3:58 pm
Hi,
dr beep wrote:
Sun Sep 10, 2017 9:22 pm
sirmorris wrote:
Sun Sep 10, 2017 5:59 pm
Also,

Code: Select all

L0237:  LD      B,(HL)          ; (7) Note. Harmless Nonsensical Timing weight.
Is exactly it :D
So the fix should be LD H, (HL)
Why is this the solution? :o 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.

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Andy Rea
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Re: Charlie's Red Ant - a ROM instruction that reads throughout memory

Post by Andy Rea » Tue Sep 12, 2017 7:56 pm

Just for fun.... :lol:
REDSINC.P
(2.11 KiB) Downloaded 21 times
regards Andy .
6 x ZX81, 1 x TS1500 , 1 x +3e, 1 x timex 2040 printer, 1 x timex 2020 cassette deck, siclair printer and some spectrum

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

Post by olofsen » Tue Sep 12, 2017 9:14 pm

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 ;)

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Andy Rea
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Re: Charlie's Red Ant - a ROM instruction that reads throughout memory

Post by Andy Rea » Tue Sep 12, 2017 9:15 pm

did i forget to mention it works very well on eightyone V1.7 :mrgreen: :mrgreen: :mrgreen:
6 x ZX81, 1 x TS1500 , 1 x +3e, 1 x timex 2040 printer, 1 x timex 2020 cassette deck, siclair printer and some spectrum

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

Post by zsolt » Tue Sep 12, 2017 11:39 pm

dr beep wrote:
Tue Sep 12, 2017 5:25 pm
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":
sirmorris wrote: * 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?

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1024MAK
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Re: Charlie's Red Ant - a ROM instruction that reads throughout memory

Post by 1024MAK » Tue Sep 12, 2017 11:55 pm

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

Mark

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

Post by sirmorris » Wed Sep 13, 2017 12:03 am

It's not a problem! It's a pet!
--=== ZXpand+ ... A more moderner all-in-one upgrade solution for ZX81 ===--
* SD/MMC storage * 32K Hires-capable RAM * AY sound chip * Joystick port * Serial *
* BASIC enhancements - plug & play * Reset button * Auto-boot facility *

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