----- Original Message ----- From: "Stephen Adolph" <[email protected]> To: "Model 100 Discussion" <[email protected]> Sent: Thursday, June 02, 2016 7:22 AM Subject: Re: [M100] Main rom using 28C256 plcc
> https://www.oshpark.com/shared_projects/wremzas3 > > all I have is the layout now. lost the design files. That's the picture I was looking for; shows the general idea. > I never tested it, and the sram is fine pitch. > anytime you have ram in the system you need to use RAMRST to protect > it during power cycles etc. So, Ive included the logic chip to do the > correct inversion. I'll have to look at the original; looks like it only has an added SMT transistor. While I'm at it I'll try to refresh my dim memory about what mods are needed (if any) for the programming adapter; ISTR that I only provided for the '512 ... m > > > On Thu, Jun 2, 2016 at 1:06 AM, Mike Stein <[email protected]> wrote: >> Boy, you'll really go far out of the way just to avoid using a programming >> adapter... ;-) >> >> Why not just a RAM chip? No external programming required at all. >> >> Actually, Steve and I considered adding an SMT RAM chip underneath the >> M100ROM EPROM socket but never finished it because of the SMT; maybe it's >> time to revisit that. Also could be used as an extra 32KB RAM bank... >> >> Wish I could find the design files; maybe Steve can find his copies... >> >> m >> >> ----- Original Message ----- >> From: Brian White >> To: Model 100 Discussion >> Sent: Wednesday, June 01, 2016 11:25 PM >> Subject: Re: [M100] Main rom using 28C256 plcc >> >> The guy basically just made it because I asked for it. He already had the >> 27C256 plcc main rom adapter up there since a few years ago, and when I >> asked him a question about it we got talking and he ended up making the SOIC >> option rom carrier and the programmer adapter to make it easier to >> re-program that after assembly, and now this 28C256 version of the main rom >> adapter. >> >> ================ >> >> He ALSO made a socketed plcc adapter for the option rom just to see if it >> would work. >> >> https://oshpark.com/shared_projects/iY7EaSqU >> >> That is tough though because there isn't *really* room for a plcc32 socket. >> It does just barely fit, by dint of:@ >> >> * Low profile plcc socket. Problem: those are surface mount. I don't think >> it will be practical to solder them with a pencil. I will try it, and I'll >> probably manage it, but I don't expect it will be practical. So I expect >> I'll also have to try with a heat gun and paste. Hopefully that is >> reasonable to offer as directions. >> >> * Sand down two side walls of the socket a little, and sand a chamfer on 2 >> edges even more, to fit the plcc socket within the ootion rom socket and not >> interfere with the pins in the option rom socket. At that point some of the >> socket material is getting pretty thin. >> >> But I did a dry fit with the current soic option rom board that had no >> compnents yet, and a low profile socket, and it looks like it will all just >> barely fit with that sanding. So the advantage there is the option rom would >> also be a nice available plcc part, and you could re-program it without a >> special "reverse-adpter-adapter" like you need for the soldered-on soic >> board. >> >> Only problem is for some reason he made it for 28F256 not 28C256. I can't >> find those anywhere except old ones on ebay. So I ordered a set of boards >> and some 28F256 from ebay, and I'll build a couple just to see if the >> process is really practical or not to expect people to do. If the soldering >> isn't too bad and the socket grinding isn't too bad and the end result fits >> and works well, then I'll ask him if he wouldn't mind making a 28C256 >> version, and THAT would be the version everyone should actually use.
