If you have access to DigiKey then you can always buy parts there (or Mouser). I used a 74HC148 as the decoder chip when I built my M100 RAM module. There are quite a lot of ways to decode the 4 Chip Enables on the RAM socket using a single IC.
These are DIP parts. AS6C6264-55PCN RAM = 1450-1036-ND - $2.43 74HC148 Priority Decoder = 296-8233-5-ND - 43c If you want to try the 74HC86 = 296-8375-5-ND - 40c Cost ~$3, however S&H would be extra. From: M100 <[email protected]<mailto:[email protected]>> on behalf of Diggy Dude <[email protected]<mailto:[email protected]>> Reply-To: <[email protected]<mailto:[email protected]>> Date: Monday, May 7, 2018 at 9:26 AM To: <[email protected]<mailto:[email protected]>> Subject: Re: [M100] 8K RAM module Well, it looks like the only 7486s I have on hand are LS. What with buying bulk parts I'll probably never use and waiting for the slow boat from China, it'll probably be more cost-effective just to buy the module on Arcade Shopper. Thanks for your help, guys! -- Jim On Mon, May 7, 2018 at 11:04 AM, Francesco Messineo <[email protected]<mailto:[email protected]>> wrote: On Mon, May 7, 2018 at 4:42 PM, Diggy Dude <[email protected]<mailto:[email protected]>> wrote: > To make sure I understand: > > Clean all pads and leads with flux.Will a flux pen suffice, or should liquid > flux be used? no, flux residue after soldering has to be removed. I use water-based flux, so I clean the boards with water and bake them to remove the water > > What specific 74HC and SRAM devices do you use? I use AS6C6264SCN memories, though they aren't guaranteed to have standby current lower than 4 uA, but I measure every module to be sure it meets this requirement. It's the only part that can be found new at this time. I have used batoches of several other SRAMs when I've found a good deal on ebay for example. I do all glue logic with a single 74HC86. > > On Mon, May 7, 2018 at 2:45 AM, Francesco Messineo > <[email protected]<mailto:[email protected]>> wrote: >> >> On Mon, May 7, 2018 at 9:08 AM, Diggy Dude >> <[email protected]<mailto:[email protected]>> >> wrote: >> > Thanks, Fugu! >> > >> > So the modern solution is a single SRAM and capacitor on a SOIC-to-DIP >> > breakout? What's the RAM chip they're using? >> >> and a logic chip (there're a few different approaches here) to combine >> the separate chip selects to a couple of addresses and a single select >> signal. My own version of the circuit uses the fewest ports possible >> (at least if nobody comes up with a different approach I couldn't >> think of). >> The RAM chip must be a CMOS static ram, 8kx8 and with low power >> standby (not all have this feature). The original 8k modules were >> specified for 4 uA max standby current, that allows the standby >> battery to keep the RAM content for over a month. Usually the suitable >> chips have L or LL in the part number, but you better check the >> datasheet for the fine details. Most of the suitable RAM chips have a >> measured standby current of 0.1 uA (often less) at 3.3V if the chip >> select are driven with the correct voltages. At these current levels, >> cleaning the soldering flux is a must. I've measured up to 15 uA of >> standby current on badly cleaned modules. YMMV. >> Glue logic *must* be 74HC family, it has a suitable current draw at >> 3.3V standby and suitable speed. In one case I've used 74AHC and it >> worked well too. >> >> > >> > -- Jim >> > >> > On Sun, May 6, 2018 at 10:29 PM, Fugu ME100 >> > <[email protected]<mailto:[email protected]>> wrote: >> >> >> >> You could try >> >> >> >> https://www.arcadeshopper.com/wp/?page_id=11#!/8k-RAM-module-for-Model-100/p/104430801/category=28313042<https://nam03.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.arcadeshopper.com%2Fwp%2F%3Fpage_id%3D11%23!%2F8k-RAM-module-for-Model-100%2Fp%2F104430801%2Fcategory%3D28313042&data=02%7C01%7C%7Cb8bb797123af403b53b708d5b43745b3%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C636613071840276763&sdata=F4%2FPkPnXMzef8DB1N50baPzETrsjrbFiag0daGnMhzI%3D&reserved=0> >> >> >> >> They have the M100 modules if you want to buy. >> >> >> >> If you want to build your own there are PCBs on OSH Park for surface >> >> mount >> >> and DIP versions. >> >> >> >> No need for any pillaging :) >> >> >> >> From: M100 >> >> <[email protected]<mailto:[email protected]>> >> >> on behalf of Diggy Dude >> >> <[email protected]<mailto:[email protected]>> >> >> Reply-To: <[email protected]<mailto:[email protected]>> >> >> Date: Sunday, May 6, 2018 at 8:13 PM >> >> To: <[email protected]<mailto:[email protected]>> >> >> Subject: [M100] 8K RAM module >> >> >> >> Anyone know where I can get an additional 8K for my 24K M100 without >> >> pillaging another M100? Let's face it: if I got another M100, I'd be >> >> inclined to leave it intact. >> > >> > > >
