Time to dig out my electronic cad software and see if I can't get a prototype board together that actually plugs in
Prince of Persia
Re: Prince of Persia
This I have to try - not sure on the availability of SRAM chips that small these days but for the sake of a few logic chips and a battery it has to be worth a try.
Time to dig out my electronic cad software and see if I can't get a prototype board together that actually plugs in
Time to dig out my electronic cad software and see if I can't get a prototype board together that actually plugs in
Re: Prince of Persia
Cool - good luck! 
If you desire some non-volatile memory, I'd recommend incorporating an EPROM or similar for that purpose, as my results with a battery were kinda disappointing (alternatively I expect there's plenty of scope for improvement on my design).
If you desire some non-volatile memory, I'd recommend incorporating an EPROM or similar for that purpose, as my results with a battery were kinda disappointing (alternatively I expect there's plenty of scope for improvement on my design).
Re: Prince of Persia
From what I can see the battery should work - similar devices are common enough on other devices and last for much, much longer (years). Looking at the battery specs on Farnell they do require a lot of charging though - casual use of the computer (a few hours a day) would not actually charge it up. I must admit a small SSD style device would be better - you can buy sdram arrays for PCs that come up with similar battery backup but they have fallen into disfavour since the arrival of proper SSDs. They normally only run to a few GB (about 8 card slots of single speed ram) but it is enough to bootstrap a computer very quickly. The problem is they were expensive (no particular reason other than profiteering I suspect).
A modern memory controller coupled with an SD card slot would certainly do the job. Even the slowest compact flash would be up to the job and the capacity is almost irrelevant. If you can only address the first 256kB (2 megabit). The smallest SD card I can find for sale is 128MB (1 gigabit) so only 512 times the size your device was intended for. I gather the addressing of it though is just down to paging of 4kB chunks (less a few bytes for the address control mapping) so the question is how much overhead are you willing to use. For 256k you need 64 pages which is only 6 bits of address map. A 1M equivalent would use a full bytes for address mapping of the pages. Extrapolating to 2bytes would give a 256M address space - 65536 of 4k pages - still within the realms of a single memory write of the d register. If we were prepared to extend to 2 words for addressing the address space becomes immense - more than we can purchase as a single card (64TB unless my sums are going badly wrong) and far, far more than we can actually use so if I were doing this as a commercial venture I would designate an SD card contents as conventional FAT32 file system files composed of sets of 4k pages and simply switch between those files. It creates an extra layer between the computer and the memory but it also allows us to make use of the much larger capacity memory devices we have now or are likely to get in the near future but then you need an interface to switch between the files and it all gets much more complicated.
I'm sat here looking at my Raspberry Pi with just 2 chips on it and thinking that with its 256Mb of RAM on board and a single functional processing chip (the second chip is for the LAN which is basically optional) there has to be something pretty much ready to roll in terms of a controller but the interfacing is the issue. The sd card readers that emulate discs don't have much on them but they conform to a pretty much standard disk control interface. The Pi cost me about £30, pricing up just the chips for your design and some DIP sockets to hold them comes to nearly the same which is frankly rather scary.
Anyway - I'll see if I can get to grips with that e-CAD software and have a play with the original design... it's been about 20 years since I last used something like it so it might take a while for the memories to come back
A modern memory controller coupled with an SD card slot would certainly do the job. Even the slowest compact flash would be up to the job and the capacity is almost irrelevant. If you can only address the first 256kB (2 megabit). The smallest SD card I can find for sale is 128MB (1 gigabit) so only 512 times the size your device was intended for. I gather the addressing of it though is just down to paging of 4kB chunks (less a few bytes for the address control mapping) so the question is how much overhead are you willing to use. For 256k you need 64 pages which is only 6 bits of address map. A 1M equivalent would use a full bytes for address mapping of the pages. Extrapolating to 2bytes would give a 256M address space - 65536 of 4k pages - still within the realms of a single memory write of the d register. If we were prepared to extend to 2 words for addressing the address space becomes immense - more than we can purchase as a single card (64TB unless my sums are going badly wrong) and far, far more than we can actually use so if I were doing this as a commercial venture I would designate an SD card contents as conventional FAT32 file system files composed of sets of 4k pages and simply switch between those files. It creates an extra layer between the computer and the memory but it also allows us to make use of the much larger capacity memory devices we have now or are likely to get in the near future but then you need an interface to switch between the files and it all gets much more complicated.
I'm sat here looking at my Raspberry Pi with just 2 chips on it and thinking that with its 256Mb of RAM on board and a single functional processing chip (the second chip is for the LAN which is basically optional) there has to be something pretty much ready to roll in terms of a controller but the interfacing is the issue. The sd card readers that emulate discs don't have much on them but they conform to a pretty much standard disk control interface. The Pi cost me about £30, pricing up just the chips for your design and some DIP sockets to hold them comes to nearly the same which is frankly rather scary.
Anyway - I'll see if I can get to grips with that e-CAD software and have a play with the original design... it's been about 20 years since I last used something like it so it might take a while for the memories to come back