On Sat, 7 Jul 2001 01:11:11 +0100 (BST), Tony Duell wrote: #> #> I am in the process of attempting to repair, with Pete Turnbull's #> invaluable guidance, an Exidy Sorcerer. #> #> The manual recites that the memory chips, depending on configuration, #> are 2104 (4k) or 2116 (16k). #> #> A casual perusal of chip sources shows that most begin their dynamic #> ram sections with 4116 chips. The only mention I have found of 2116 #> chips is in a reference to the original IMSAI memory board. #> #> So, my questions are: Are 2116 chips 3-rail? Are 4116 chips # #As far as I can see, yes the 2116s are 3-rail and have the same pinouts #as 4116s. A lot of the time, various manufacturers made very similar RAM #chips with slightly different numbers (another example is the 2016 2K*8 #SRAM which is very similar to the 6116). Sometimes there were slight #timing differences between various manufacturer's chips, often it doesn't #matter. # #I would be very suprised if the Sorceror doesn't work with 4116 DRAMs in it. # #> equivalent? Does anyone have a source for 2116 chips, if they are not #> equivalent? What about 2114 static ram (used in the video section of #> the Exidy)? Same problems? Were they all three rail? # #The 2114 SRAM is single-supply rail (+5V only). Again, it was made by #several companies (but I think most of the time it was called the 2114). #It also happens to be the chip I've had the most failures from :-) # #> #> A general lecture on the nature of old memory chips and their use and #> selection would be very helpful (hint to Tony Duell). # #Most of the time, RAMs are pretty generic. Match up the capacity, type #(SRAM or DRAM) and number of pins, and you're close to finding a match :-) # #In general, SRAMs were single-rail, +5V only. DRAMs were often 3-rail up #to and including the 16K bit parts. There were single-rail 16Kbit DRAMs, #but they are not that common, and they came out later than the 3 rail parts. # #Most DRAMs have a multiplexed address bus (that's how you fit a 16K RAM, #needing at least 14 address lines, 1 data line, 1 write enable line ,and #3 power lines into a 16 pin package). You send the address in 2 parts and #bring RAS/ and CAS/ low as appropriate. Some older 4K DRAMs, in 22 pin #packages, have a normal address bus with 12 separate pins. Those 22 pin #DRAMs are odd in othter ways, like needing a strobe pulse at 12V levels. # #I am not sure exactly what you want to know, though. If you can say what #information you need, I'll try and dig out the databooks. # #-tony This answers most of my questions, thanks. One further question. What is the difference between "static" ram and "dynamic" ram, since both are "volatile" ram? Or, putting it another way, what is "static" about "static" ram, since it changes as well? Louis

Another simple question. When a standard single-rail 2716 is installed in a computer, what do you do with the Vpp pin? Tie high, low, or leave alone? If tying, what, if any value resistor should be used?

Connect Vpp to Vcc (+5V), with no resistor in series (i.e. a direct wire connection). That's what I've always done anyway. With most EPROMs you link Vpp to +5V in read mode. Mask ROMs obviously don't have Vpp line, and the pin is normally either unconnected (in which case you can do what you like with it, within reason [1], including connecting it to +5V), or sometimes it's another chip enable input. The latter is often level selectable by an option set by the programming mask (i.e. when the chip is mask-programmed, as well as the data being defined, the active level of the chip select lines (active high or active low) can also be set). Of course if the mask ROM has an active-low enable pin there, you have to connect it to ground. What you need are the data sheets for the EPROM you are using. Most semiconductor companies put the data sheets of their current parts on the web in pdf format. Very rarely are obsolete data sheets made available in this way. It's worth obtaing all the old data books that you can find, since they contain data sheets for the chips found in classic computers :-) -tony

Is that also why static RAM is so much faster? Peace... Sridhar On Sat, 7 Jul 2001, Tony Duell wrote:

from one thoroughly voltage-abused board of small SRAMs, I've got very few that

--- Tony Duell <ard(a)p850ug1.demon.co.uk> wrote: I, too, have had these fail numerous times. Much more so than other SRAMs or any DRAMs. The only ones that came close were from the same era: 4096 DRAMs - I have them on some LSI-11 boards and inside a Z-80-based Gorf. When I first got all the parts together to refurb a full-sized Gorf machine, the internal tests showed a memory fault on one of the DRAM boards, covered in 4096 chips. I use the LSI-11 CPU, a COMBOARD (for its memory mapping/DMA engine) and a Fluke tester to check the 4K DRAMs - plug the COMBOARD on the Qbus, put the test RAMs on the LSI-11 board, plug the Fluke emulator/tester in the 68000 socket on the COMBOARD, fire it all up, hit the DMA enable bit on the COMBOARD, then through the Fluke, test a range of 68K memory that corresponds to the appropriate range of Qbus memory addresses and voila - a 4096 tester with about $25K-new-cost worth of test gear. (The Qbus COMBOARD memory map is divided into 4 regions, RAM, shared-memory, I/O and ROM. There are 22 bits of 68K space available to map each and every Qbus location into some valid local address. Who needs mapping registers! No FUBAR on a Qbus!) The first COMBOARD used 2114 SRAMs because they were more reliable than Intel's DRAMs of the day (plus the XC68000 would occasionally enter a microcode fault and reset, causing Z-80-style bus-driven refresh mechanisms to pause too long, letting all the bits leak out).

-ethan ===== Visit "The Seventh Continent" http://penguincentral.com/penguincentral.html __________________________________________________ Do You Yahoo!? Get personalized email addresses from Yahoo! Mail http://personal.mail.yahoo.com/

--- Richard Erlacher <edick(a)idcomm.com> wrote: > > The first COMBOARD used 2114 SRAMs because they were more reliable than

This is slightly before my time, but I was told that the earliest 68000 designs that used DRAMS, used a derivative of the Z-80 scheme because the designers of the time were used to it. I didn't mean to imply that the 68K had some kind of magical in-built DRAM refresh support.

The microcode faults I was told about for the XC68000 (not MC68000) would

lock things up tight for dozens of clock cycles, then go right back at it, as it nothing ever happened. It was strictly internal to the CPU and caused by bugs in the first run. Your software never knew what hit it unless it was checking timings against an external clock.

By the time I personally touched a 68000, these kinks were long worked out (except for knowing that one needs to put low-ohmage resistors (30-60 Ohms) in series with the refresh lines from a DRAM controller when attempting to refresh several dozen DRAMs (4164s in this case). I chuckled when I saw those same resistors in the front memory cartridge of an Amiga 1000. They at least got them in there by the time their production started. I added hundreds of 68 Ohm resistors to the first production run of COMBOARD-II rev 0s. Once one of those came back from the soldering house, I think it took 3 hours of bench time to apply all the ECOs. Good thing they were already expensive. -ethan ===== Visit "The Seventh Continent" http://penguincentral.com/penguincentral.html __________________________________________________ Do You Yahoo!? Get personalized email addresses from Yahoo! Mail http://personal.mail.yahoo.com/

I am in the process of attempting to repair, with Pete Turnbull's invaluable guidance, an Exidy Sorcerer. The manual recites that the memory chips, depending on configuration, are 2104 (4k) or 2116 (16k). A casual perusal of chip sources shows that most begin their dynamic ram sections with 4116 chips. The only mention I have found of 2116 chips is in a reference to the original IMSAI memory board. So, my questions are: Are 2116 chips 3-rail? Are 4116 chips equivalent? Does anyone have a source for 2116 chips, if they are not equivalent? What about 2114 static ram (used in the video section of the Exidy)? Same problems? Were they all three rail? A general lecture on the nature of old memory chips and their use and selection would be very helpful (hint to Tony Duell). Thanks, Louis