One more kick at the can: ----- Original Message ----- From: Brian White To: Model 100 Discussion Sent: Thursday, June 02, 2016 11:55 AM Subject: Re: [M100] Main rom using 28C256 plcc
As I said, to each his/her own and we do have somewhat different goals and perspectives. My goal was to offer a cheap and simple adapter for around $10 in parts that could fix the Y2K problem in the old M100s and for little or no extra cost or effort add an option ROM such as TS-DOS for example; most importantly like most M100+ addons and accessories it requires no soldering on or modifications to the M100's main board and could easily be installed by almost anyone. On the off chance that a user would want to reprogram the EPROM an adapter would not be a big issue IMO; this is commonly done elsewhere when replacing chips like the 2532, 2332/64, 68764 etc. which, although electrically compatible, many programmers can not do due to a non-'standard' pinout. Your goal appears to be to offer separate modern replacements for both the system and option ROMS and avoid having to use an adapter at all costs, even if it requires modifying all M100s by removing and replacing the ROM socket. So, different perspectives, but I don't get at least one of your points: ==== So ideally it would be good to be able to remove the new standard EPROM to reprogram it. So that means a socket for the new EPROM. ---- This the main part that I don't get; if you're prepared to remove the original socket and solder in the adapter in order to put the EPROM in a socket why can't you do exactly the same thing with the M100ROM? What AM I missing here? Being able to re-program without de-soldering or using an adapter would be indeed be nice, but having to desolder the socket on the M100 board seems like the worse of two evils to me... ==== Then again, it's ALSO true that having the option to put the original mask room back in (not merely reflashing an image that purports to be the same) is also valuable. Especially when it's 15 years from now and the eeprom is losing bits and you just got this thing and don't know what these wierd hacks are some previous owner did. Also for reference, like when I was trying to figure out why pg designs menu.ba was not working yesterday. So that means a socket on the motherboard. ---- Indeed, sounds like an argument for the M100ROM. ;-) ==== There's no way there's room for two sockets and an adapter and a chip between the motherboard and the keyboard. But if you say you normally plug your adapter into the original socket on the motherboard, then that proves there is room for one socket. ---- Obviously there's room for one socket; I suspect that by using a thinner PCB and using machined socket pins it *might* just be possible to keep the system socket and make the EPROM removable, but I never really investigated. So far it's never really been an issue. ==== You're right that a programming adapter would be pretty easy. ---- You get the essential basic part for free... ==== Except I also would prefer to use eeprom instead of uv, which your board is not configured to use, and, it would also require adding a pullup and a jumper header to your board to handle WE or else you couldn't actually program with just an adapter, you'd need a test clip. That's all doable and everything would fit the same, but that's not what your board actually is. (Actually, I like the option to use either uv eprom or eeprom, in case one or the other lasts more years before losing charge.) And I also would like, if possible, eventually, to be able to just buy the same part for both main and option rom. ---- No argument there; personal preference and priorities... ==== So, if there was a 28C256 dip28 in the main rom, then could we get a 28C256 dip28 on an adapter in the option rom? Actually yes. I have old commercial option roms which are cerdip28 squeezed onto an adapter pcb. You might even just barely manage to get a pullup resistor and jumper header on there for write enable. Though I am finding out the hard way that a programming adapter to grab those half-hole edge contacts is not so easy to make. Far far better to either remove the eeprom, or use a test clip Well there is no room for a dip socket for the option rom so that just leaves a test clip. Why make people buy a test clip if there is a way without it? ---- Yes, the option ROM presents some different challenges which I'll leave you with. A pity that we can't get those funky flexible ROMBO adapters any longer... ==== As for the option to load an option rom on the same chip as the main rom and bury it inside the case, and render the option rom socket unusable; That option is interesting and cool in the abstract, but nothing I would want to do. I want to be able to snap in actual old roms, and play with loading different ones from images, and eventually maybe even hack on them. ---- As I said, here's where we have different goals and perspectives; No problem, just don't use the option and only use it to fix Y2K etc., and plug whatever you like into the Option socket. For tinkering with the ROM images I'd rather use a REX or finish the M100ROM design with RAM (that's how option ROMs were usually created and debugged); IIRC both solutions also give you extra system RAM and also (at least in the case of REX) let you tinker with the *system* ROM image in RAM . No fiddling with removing and inserting different option ROM adapters/chips at all! Anyway, good luck and have fun, but I'd appreciate if you could clarify for me the difference between soldering your adapter to the system board with a socket for the EPROM vs. doing the same thing with the M100ROM? m
