I want to announce a new project which is near production. Me and some other people on the german forum wanted to have their own ZX80 board. After several discussions we decided to produce a modern board, which looks like ZX80 but supports some new memory ICs and some new features. And the goal was to have CAD data manufactured board with stop mask and silk print which Grant Searles data does not support.
So optical it is nearly identical to the ZX80 board. It will be produced with white stop mask and black silk print which looks really nice and more high-end like an example in this picture:
So the board completely fits into the original ZX80 case (mounting holes, dimensions, connector placement, height of board/components).
Following add-on's or modifications are done:
ZX80 connector, pin 23b => /ROMCS is wired to this pin and /ROMCS is connected internal via a resistor
so /ROMCS can be overdriven by external components like ROM attachements or similar - this is optional via a jumper (pin can be left empty like in original)
- so external modules like RAM extensions, printer and so on can be used with it (depending on drivers, ROM version, for more read further)
voltage regulator - here can be used either the classic 7805 linear regulator with a heatsink or a switched regulator with additional filter / inductor
keyboard - here the original ZX80 keyboard foil can be used as well as smd tactile switches, very small have found them with only 1.5mm height (0.06 inches)
see picture below:
ROM - here can be used a list of several eproms and eeproms:
2732 (EPROM, 4k x8)
2764 (EPROM, 8k x8)
27128 (EPROM, 16k x8)
27256 (EPROM, 32k x8)
27512 (EPROM, 64k x8)
2864 (EEPROM, 8k x8)
28128 (EEPROM, 16k x8)
28256 (EEPROM, 32k x8)
The advantage of the EEPROMS is, they can be programmed or reprogrammed with a running ZX80, only a first initial programming with the 4 k ZX80 rom is necessary. There is an additional switch (hex coded with 16 positions) which overdrive the address lines at the EPROM or EEPROM. This allows to put additional drivers inside the ROM and to switch between different OS. The 27128 can be programmed with 4k ZX80 rom and additional drivers at address $0000-$1FFF and for example ZX81 ROM at $2000-$3FFF. Via the switch you can choose which ROM to "boot". Maximum useable ROM size is 16k as original address decoding is not changed (just the ROM is not mirrored in this area). Same is for EEPROMs.
The disadvantage is that the old 2532 EPROM (different pin out) is not supported. But these are really rare to get (either unprogrammed) and today most programmers wouldn't support that pin out.
The price for the board with double europe size format (204 x 155.5 mm or 8 x 6.125 inches) double sided, plated, with stop mask and silk print would beRAM - here can be used the original two 2116 (1k x4) or up to 16k RAM
2 x 2114 (SRAM, 1k x4)
1 x 6264 (SRAM, 8k x8)
1 x 62256 (SRAM, 32k x8)
Maximum 16k RAM can be used as original address decoding is not changed, just less mirrored if bigger RAM is inside ($4000-$7FFF).
The 2114 and 8 bit RAM are placed over each other so you have to decide wether to use 2114 or for example 62256. But you can use small socket "lines" instead of sockets so this can be changed back at a later time (up to you).
Alternativ could be an external RAM extension, just used in case you want it by connecting to the ZX bus on the backside (edge connector).
The ZX81XRAM is suitable for ZX80 as well
If I have minimum 10 orders for this board this price will go down to EUR 25,00 for the same boards.
So now I have 7 preorders on the german board, if we can find 3 more here the board would be available for EUR 25,00 (GBP 21.00).
So if you are interested please give me a feedback in case you are interested in buying this board.
The plan is to finish the routing till 15th of may.
After I do a first prototype (industrial produced but single board) to eliminate eventually bugs on the board to have at last a bug-free board.
I think this is necessary due to it's complexity (about 100 components, not including tactile switches if used, 700 single pins or pads and more than 500 nets) and I think everybody would be more interested with a board not seen any cables, cuttings and so on.
Approximately in end of june 2013 the board would be available for delivery in a second batch with more boards.
So please let me know what you think.