This was the original prototype:
This prototype used a W29EE011 and was read only, meaning it still required a programmer and dismantling the spectrum to change the contents of the chip. This board has now been dismantled, and a second prototype built.
The second prototype used an AM29F010B 128kB flash ROM:
This prototype was again built on tripad board, this flash ROM is a PLCC package so is plugged into this prototype through a PLCC-DIP adapter. The final board used a PLCC socket instead of the DIL socket.
The flying leads are terminated with miniature crocodile clips. These are clipped to short lengths of wire that have been soldered to relevant points on the motherboard. The production board used IC test clips to allow the flying leads to be attached to the relevant legs of the CPU and RAM with no modification to the motherboard.
Assembling the boards:
The prototypes for the second edition flash board:
These prototype PCBs were manufactured by Futurlec and the components sourced from the same place. The boards are of a good quality and reasonably priced for a small prototype run - in fact they unexpectedly shipped all the spare boards produced despite me only paying for two which is a service many places charge extra for.
I was however much less impressed by the components as the flash chips they sent were used and had protection bits set! I complained and they sent replacements which were the same. I can't grumble too much as it means I got two spare chips for nothing but it was a definite inconvenience. My EPROM programmer is not able to clear the protection bits on these chips so I had to breadboard a circuit with a microcontroller to toggle the high voltage signals on the relevant pins to unlock the chips. I would not recommend buying flash chips from Futurlec!
The new design uses a 29F040B which is a 4 megabit flash ROM. This means it has four times the capacity of the 29F010 used in the original flash boards and can consequently hold up to eight different operating system ROM sets, or thirty two individual 16kB ROMs!
The other main difference is that this board does not have the design flaw present in the original board which necessitated the addition of a write enable jumper in series with the !WE flying lead to prevent the ROM being corrupted when reprogramming the flash ROMs of external interfaces.
This board has been designed such that the flash responds to different programming codes (by altering the interconnection of the data lines) so that only the flash programming software for this board will unlock it for writing.
A new flash programming tool has been written for these new boards as the new higher capacity flash chip has larger erase sectors (64k as opposed to 16k) so full use is made of the 128k RAM paging to allow individual 16k pages to be re-flashed. The UI has been completely revamped too and now also supports loading ROM images over the network if a spectranet is present.
Sneak peek of the new programming utility:
I plan to add support for the original flash boards to this tool so that anyone who bought one of the original flash boards can make use of the new program rather than just a handful of people who got preproduction prototypes of the new board