Question, how do I write to memory through the expansion port? Possible?

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sl07h1
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Joined: Mon Feb 22, 2021 7:16 pm

Question, how do I write to memory through the expansion port? Possible?

Post by sl07h1 »

Hi gurus.

I think the title says everything. I have a Raspberry 3 and a couple of bad memory packs that I could destroy without remorse, is it possible to build some circuit and use the Raspberry GPIO to load a .p file directly to memory? there's something done?

Thanks in advice!
terrymr
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Re: Question, how do I write to memory through the expansion port? Possible?

Post by terrymr »

The raspberry Pi uses 3.3v logic rather than 5v so that will be a bit of a problem. Beyond that in theory you could signal the z80 that you need access to the bus via busreq wait for the busack signal then load your program into ram. Then you’ll need to feed the z80 instructions to jump to whatever the rom does after loading a program from tape.

Or something like that.
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Paul
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Re: Question, how do I write to memory through the expansion port? Possible?

Post by Paul »

A friend of mine uses the busrq and busack at the moment with the help of an Arduino because of it's 5V bus.
That works good and you can modify ram without problems. So loading software into the ZX81 or other Z80 machines is no problem.
The thing we are developing will become a diagnose module so we can analyze a Zeddy or Speccy without opening it.
To my knowledge there is no loading or saving device existing or under development using the bus.
Kind regards Paul
In theory, there is no difference between theory and practice. But, in practice, there is.
sl07h1
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Re: Question, how do I write to memory through the expansion port? Possible?

Post by sl07h1 »

Thanks for the responses, guys, I will try Arduino then, I assumed that Raspberry used 5V logic. Where can I find more info on how to do the "charging" of the bytes? I mean the process itself, I know close to nothing about it, Where can I find some specs for the expansion port?? I have searched but no good answers.

Thanks in advice!
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1024MAK
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Re: Question, how do I write to memory through the expansion port? Possible?

Post by 1024MAK »

The details on the expansion connector, more often referred to as the edge connector are here as well as in a lot of other places.

There is a schematic diagram of the circuitry in this post. Although this version has the French video circuitry for the input to the modulator the rest is basically the same for all ZX81, TS1000 and other versions built using the same PCBs.

As for your other question, I’m not quite sure what you are asking.

Mark
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bola_dor
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Re: Question, how do I write to memory through the expansion port? Possible?

Post by bola_dor »

Paul wrote: Wed Aug 25, 2021 7:36 am A fried of mine uses the busrq and busack at the moment with the help of an Arduino because of it's 5V bus.
That works good and you can modify ram without problems. So loading software into the ZX81 or other Z80 machines is no problem.
The thing we are developing will become a diagnose module so we can analyze a Zeddy or Speccy without opening it.
To my knowledge there is no loading or saving device existing or under development using the bus.
Kind regards Paul
I whant one of that things !!!!
Are you making it able to scan a rampack attached to it.. that would be usefull...
Ernesto
ZX80 USA, ZX81UK, ZX Spectrum, ZX Spectrum+, ZX Spectrum 128+ UK, ZX Spectrum +2/A, Sinclair QL, CZ1000, CZ1500, CZ2000, CZ1000Plus, CZ1500Plus, CZ Spectrum, CZ Spectrum Plus, TK83, TK85, TK90X, TK95. TS2068. And more to come :D
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Paul
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Re: Question, how do I write to memory through the expansion port? Possible?

Post by Paul »

If the RAM pack, unlike the Sinclair types, has the edge connector through then our little diagnosis module can be attached behind the RAMpack as long as a Zeddy is first in the Row. It's not designed for it, but will shure work and test the memory for reliability as well as the Rest of the Zeddy
Rampacks on their own will not be tested by our device.
To be honest, I don't use old RAM packs. Once you have a working Zeddy, go for a zxpand (which can't be tested by our diagnosis module) or better a built in memory expansion. SRAM is so much better than DRAM. Or when using DRAM, make shure it's working with 5 Volts only.
The design of Sinclair negative voltage circuits is, how to say, somewhere between optimistic and adventurous.
In theory, there is no difference between theory and practice. But, in practice, there is.
bola_dor
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Re: Question, how do I write to memory through the expansion port? Possible?

Post by bola_dor »

Paul wrote: Wed Aug 25, 2021 7:37 pm If the RAM pack, unlike the Sinclair types, has the edge connector through then our little diagnosis module can be attached behind the RAMpack as long as a Zeddy is first in the Row. It's not designed for it, but will shure work and test the memory for reliability as well as the Rest of the Zeddy
Rampacks on their own will not be tested by our device.
To be honest, I don't use old RAM packs. Once you have a working Zeddy, go for a zxpand (which can't be tested by our diagnosis module) or better a built in memory expansion. SRAM is so much better than DRAM. Or when using DRAM, make shure it's working with 5 Volts only.
The design of Sinclair negative voltage circuits is, how to say, somewhere between optimistic and adventurous.
I have them all, a ZXspand+, a myself made SRAM module and several Sinclair 4116 based modules..
An edge connector with a rom tester would be interesting but I see is not in your plans.. I am trying to resuscitate some old Sinclair and clones I have..
nothing rational..
Ernesto
ZX80 USA, ZX81UK, ZX Spectrum, ZX Spectrum+, ZX Spectrum 128+ UK, ZX Spectrum +2/A, Sinclair QL, CZ1000, CZ1500, CZ2000, CZ1000Plus, CZ1500Plus, CZ Spectrum, CZ Spectrum Plus, TK83, TK85, TK90X, TK95. TS2068. And more to come :D
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