Sinclair ZX80 / ZX81 / Z88 Forums

ZX81 Chip Pin-outs


Note the notch cut-out at the top of the chip. Pin 1 can also be designated by a white dot marked next to it.

RAM Mark

Sinclair ZX81 ULA I hope these pin-outs are helpful to those who do not yet have this information etched in to their minds yet
If you spot any errors, please let me know so that I can correct them.
Also note that the ROM socket and RAM socket may be bigger than the size of the chip actually fitted. These pin-outs are for the chips, not the sockets.

1 bit X 16k 4116 DRAM
As used in both Sinclair's 16k byte RAM pack and many other 16k byte RAM expansions. Mark

Never come across PSRAM before - looks cool. Anyone know where you can buy it?

I hate DRAM, but find the capacities of SRAM to be quite disappointing so this stuff looks interesting.

Great stuff, Mark! Thanks

Great, thanks

For the 2114, i think there are two of them, do the pins for both chips go to the same place?

As for the RAMs the address lines and data lines can be swapped in any way, you can not trust that A5 goes to A5 or that I/O3 goes to D3 or D4.

yalokinh wrote:For the 2114, i think there are two of them, do the pins for both chips go to the same place?

If you are using 2114 SRAM chips, two are needed. One does 4 bits of the 8 bit byte, the other does the remaining 4 bits of the byte. Connect the ten address lines of both to the A0 - A9 address lines of the Z80 CPU.

As PokeMon says, 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

Note that the ULA named pins do have to tie up with ("connect with" either directly or via the resistors) the similar named Z80 CPU pins as per the schematic diagram.

The system will work fine, as the CPU can read and write data to the RAM.

Note this mixed up connection system will not work for the ROM. It only works for static RAM chips.

Mark

Edited to add a word that I missed out (work) in the last sentence

ah cool, learning lots!
Thanks