Prototyping Blog page
here be found pictures of a 128 board in distress...
Topside overall view - major differences being lack of RAM, Reset button, new PSU, new ROM layout, modified decoding. The SRAM will sit in EPROM socket 3 with a daughter board to provide the extra 4 pins required. The multiplexed bus system is working after modification to remove redundant funtionality mostly concerned with RASCAS generation and video timing.
A closer view ...
Its not the most exciting in software terms - at the moment it flashes a LED every second. A 14.xxxMHz crystal osc module gives about 3.8MHz at the z80 (and incidentally a 50Hz rtc signal from one of the original clock dividers), The only other peripheral implemented at present is the keyboard port - and that may not survive, it would be more useful as an input port from the propeller which can use USB/PS2 keyboards.
The new PSU input for prototyping - to be replaced with onboard switched regulator over where the TV modulator sat. The relay I bought to use in my 48K Lynx back in 1984 - it is brand new - it has taken me 29 years to put it into a Lynx board.
Nice old stock sockets I had in the box, more colourful old stock to come, along with some OA90 diodes and GE germaniums if I can find some circuit to take them.
The ROM banking - a 512kbit EEPROM switchable on A15/14 between passthru from z80, High, or Low allowing multiple ROM images at 64kB, 32kB, 16kB
The darkside of the board, not tidied yet just tacked. Only ten or so wires so far, what doesn't come across is the 20 cuts.
I like a few tants hanging around the place.
this is a slave 800k drive I made with John's assistance and generosity - the BBC cumana psu fitted easily into the space where the Lynx supply used to go. I printed the logo on my superb HP Photosmart 3100 - which isn't supported by Windows Server 2008 - ho hum I won't say a word... so no instead I had to draw it very badly and colour it in crayon. Do I get extra points for being 'Leisurely' John?
... OK Guys Thats All For Now ....
... Thanks for your time, any comments welcome ....