m1-not (again, again!)

Discussions about Sinclair ZX80 and ZX81 Hardware
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sirmorris
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m1-not (again, again!)

Post by sirmorris »

Can an m1-not circuit be external? Or does it have to be 'behind the resistor fence' (nice ;¬)

C
BlackCanyonFX
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Re: m1-not (again, again!)

Post by BlackCanyonFX »

"Can an m1-not circuit be external? Or does it have to be 'behind the resistor fence' (nice ;¬)"

? and your point is what ? Since I am the only one on this board to use , or better still, to have coined the phrase,"Behind the resistor fence".

I guess I must ask yet again, Am I being mocked? And if so, WHY?

Perhaps I am being a bit thin skinned or perhaps I just don't get european humor.
Enlighten me, if you will, 'cause I'm not going away.
Cheers, GTB
"If you are not one of us, go away" - Don Lancaster
Preface to, "Son of a Cheap Video" 1980
Prime
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Re: m1-not (again, again!)

Post by Prime »

BlackCanyonFX wrote:"Can an m1-not circuit be external? Or does it have to be 'behind the resistor fence' (nice ;¬)"

? and your point is what ? Since I am the only one on this board to use , or better still, to have coined the phrase,"Behind the resistor fence".

I guess I must ask yet again, Am I being mocked? And if so, WHY?
I don't think SirMorris' intention was to mock you at all, I actually think the phrase is pretty descriptive of what goes on in the ZX81 hardware, and he was just using that phrase to describe just that.

Cheers.

Phill.
BlackCanyonFX
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Re: m1-not (again, again!)

Post by BlackCanyonFX »

Hey Phil,
I don't mean to get all uppity.
I just don't get the drift of the post. Guess I am a bit tired.
I appologize. I have some fun stuff coming for ya all and I should just shutup and relax.
Sorry about the puff,
GTB
"If you are not one of us, go away" - Don Lancaster
Preface to, "Son of a Cheap Video" 1980
BlackCanyonFX
Posts: 35
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Location: Black Canyon City, AZ

Re: m1-not (again, again!)

Post by BlackCanyonFX »

PS...Sir Morris
Sorry, actually, after re-reading all this...really, really sorry. Big oops on me.
My appologies for my stupidity,
GTB
"If you are not one of us, go away" - Don Lancaster
Preface to, "Son of a Cheap Video" 1980
sirmorris
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Re: m1-not (again, again!)

Post by sirmorris »

@ GTB- I can't pretend I'm not a little disappointed, but I'm sure I'll get over it..!


So the question remains - can you implement an m1not - oooh let's say for the sake of argument - in the GALs of the ZXpand?

C
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Andy Rea
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Re: m1-not (again, again!)

Post by Andy Rea »

i'm pretty sure that it can't be done externally (not safely anyway)

to perform the NOTM1 trick we are looking for the following conditions

A15 - high
A14 - low
M1 - low

now M! and A15 are used to detect video cycles, so we need to over-ride either one of those signal, it doesn't matter which one.

however since as both A15 and M! signal lines are directly connected from CPU to ULA there is no way of safely over0riding the signal.

trying to alter the data on D6 is also futile as that is 'behind the fence' the only other signal you could play with is HALT but again that is directly connected between ULA and CPU so can't be overiridden safely.

looks like you either need to cut a track or lift a pin on either the CPU (probably the best option) or ULA and insert some logic internally.

Regards Andy
what's that Smell.... smells like fresh flux and solder fumes...
sirmorris
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Re: m1-not (again, again!)

Post by sirmorris »

Aah ok, I kind-of thought that would be the case :¬\

Damn Sinclair and their cleverness!
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