ZX81 Chip Pin-outs

Discussions about Sinclair ZX80 and ZX81 Hardware
peepee
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Re: ZX81 Chip Pin-outs

Post by peepee »

Thank you for the zx81 chip pin=outs, I have printed out the info and put it in my Sinclair file, they are references which I didn't have. ...peepee.

HollyJuster
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Re: ZX81 Chip Pin-outs

Post by HollyJuster »

Hi..i am new user here. As per my knowledge the actual order of the connections is not important. What do we mean by this? Well, as the Z80 writes data to the RAM , and the RAM does not care where that data is stored, it makes no difference if the address lines are mixed up. For example you can route Z80 CPU A0 to RAM A2, CPU A1 to RAM A1, CPU A3 to RAM A0, CPU A4 to RAM A3 etc. as long as all the address lines connect to the "lower" address lines (A0 - A9) of the CPU.You can do the same for the data lines (CPU D0 - D7) to the RAM I/O1 - I/O4. Route four of the data lines (CPU D0 - D7) to the I/O pins of one 2114, and route the remaining data lines to the second 2114 chip

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PokeMon
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Re: ZX81 Chip Pin-outs

Post by PokeMon »

You are right about this but it doesn't make too much sense to do so for two reasons.
At least you have to know in schematics which pin is connected to what to look for possible malfunctions/repair.

Second is, when you ever plan to replace a ram with a flash rom later, you will byte in your ass when trying to change later.
My first ram extension was made with mixed address/data lines for more easy routing but I regret later when trying to use my pcb board for using a flash rom or EEPROM to change it to a programming device with only some minor expected modifications. The modifications where much harder due to scrambling address and data lines.

So I would always recommend to follow the data sheets properly in the proposed way how to use address and data lines even it is possible to swap them when using a ram device.

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zx81jens
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Re: ZX81 Chip Pin-outs

Post by zx81jens »

Hey HollyJuster!

Welcome to the Forum :-)

Greetings
Jens (German ZX-TEAM)
eyerything will be okay in the end.
if it´s not okay, it´s not the end.

and: uıɐbɐ ʎɐqǝ uo pɹɐoqʎǝʞ ɐ ʎnq ɹǝʌǝ ɹǝʌǝu ןןıʍ ı

cbmbsw
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Re: ZX81 Chip Pin-outs

Post by cbmbsw »

made a pdf of marks work, for archieving reasons...
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ZX81 Chip Pin.pdf
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povvercrazy
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Re: ZX81 Chip Pin-outs

Post by povvercrazy »

I know I'm late to the party but I notice there is no pinout for a internal 16k 62256 28 pin chip or is that considered a mod?
Also my '81 (Issue 3) has a 24 pin toshiba TMM2016AP-15 ram chip and the pin out doesn't match, I'm cross referencing a schematic drawn by Ron Reuter SRC 049 and the 2114s dont match up to your pinouts?
Are your pinouts for an issue 1 ??

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RetroTechie
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Re: ZX81 Chip Pin-outs

Post by RetroTechie »

Just go with the ZX81 schematic, and datasheet for the exact RAM IC's that are fitted. These are either 2 pieces 1K*4 bit RAMs, or a single 1K*8 bit RAM (or 2K*8 in the case of a US-sold TS1000, with LK1 wire link in LK2 position). All those RAM chips are static RAMs and have standard pinout. So unless you're looking for timing diagrams, supply current info or such, a datasheet of ANY similar RAM chip will do.

Any other documentation will either line up with that, or is incorrect.
povvercrazy wrote:
Mon Apr 10, 2017 5:36 am
I know I'm late to the party but I notice there is no pinout for a internal 16k 62256 28 pin chip or is that considered a mod?
Yes that's a mod, no ZX81 ever came from factory with >2KB RAM. 62256 is a 32K*8 chip btw, only half the memory is used because 16K*8 SRAMs don't exist or impossible to find.

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RetroTechie
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Re: ZX81 Chip Pin-outs

Post by RetroTechie »

Just checked the above pdf. For some reason cbmbsw included the pinout of a 2K*8 PSEUDO-static RAM (a dynamic RAM with static RAM like pinout), which is USELESS.

The only ZX81's that came from factory with 2K installed were TS1000's, and the RAM chips used there are standard pinout 2K*8 static (not pseudo-static) RAMs. Which are 24 pin IC's like the 1K*8, not 28 pin.

The only 28 pin RAMs you might encounter inside a ZX81 will be 8K*8 or 32K*8 SRAMs, which by definition are modifications as no ZX81 ever came from factory with such a chip inside. The external RAM packs on the other hands used 16K*1 DRAMs.

Imho only an idiot would even consider using a pseudo-static RAM for a mod like this. :twisted: And yes, I've yet to encounter a pseudo-SRAM in a ZX81... ;)

What IS a given though, is that you may encounter many different brands/manufacturers of chips inside a ZX81 (or other Sinclair machines like ZX Spectrum). Sinclair was well known for fitting whatever chips they could get their hands on, as long as they fitted the boards & worked.

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1024MAK
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Re: ZX81 Chip Pin-outs

Post by 1024MAK »

povvercrazy wrote:
Mon Apr 10, 2017 5:36 am
I know I'm late to the party but I notice there is no pinout for a internal 16k 62256 28 pin chip or is that considered a mod?
Also my '81 (Issue 3) has a 24 pin toshiba TMM2016AP-15 ram chip and the pin out doesn't match, I'm cross referencing a schematic drawn by Ron Reuter SRC 049 and the 2114s dont match up to your pinouts?
Are your pinouts for an issue 1 ??
I did not include the 62256 SRAM (as RetroTechie says, it's a 32k byte chip) as it was not originally fitted in ZX81s or expansions.

The naming of the pins on the chips is as per the manufacturers data sheets (except for the ULA, where I used schematic circuit diagrams and checked a real ZX81 issue 1 PCB).

With some signals, on some types of chip, the designer of the system, or the circuit board designer may not connect the pins as you may expect.

With RAM chips, it does not make any practical difference if the CPU data pin D0 (data bus line 0) actually goes to the RAM chip pin that is labelled D8. As long as all the data bus lines from the CPU end up at the RAM data bus pins.

The same applies to the address lines (A0, A1, etc...). However there are some restrictions if dynamic RAM (DRAM) is being used and the CPU is providing DRAM refresh.

If the connections you are referring to are the tracks on the PCB, or a schematic drawn up showing the PCB connections, yes there will be differences. Sinclair (and other manufacturers) used the easiest PCB layout to keep the cost low. So often this means that the RAM is not wired as you may expect. This does mean that the pin-out for the socket on the PCB will not be the same as the manufacturers data sheet pin-out!

If you have found something different, can you supply details, or point me to the different details (a link...)

I included the pin out for the MK4816 Pseudostatic RAM in case any were used, and so that people could see why the PCB has provision for a 28 pin chip with an unusual pin out.

Mark

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povvercrazy
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Re: ZX81 Chip Pin-outs

Post by povvercrazy »

Ah thanks for the explanation Mark that might explain the discrepancies I'm seeing, my '81 has a '2016. Will triple check thanks

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