At 2003-02-26 09:29 -0800, Robert Smith wrote: >Installed in the system is a Godbout EconoRam II memory board 8K x 8 that I >built from a kit. I also have at least one (maybe two) kits for these >boards still sealed in factory boxes that I never got around to building. >(Ambitious plans to take the system to 24K bytes of RAM!!!, no follow >through). The one that I built is fully socketed and has provisions for two >7805 regulators. > >Each of these boards sports 64 each National Semiconductor MM2102AN-4L (8K x >1?) Static? RAM chips. Everything seems to bear a 1977 date code.
Those chips are probably the same as the Intel 2102's so 1K*1 SRAM's. You would use 8 in parallel to get 1K*8 (like in my TRS-80's video RAM) and 8 of those banks to get 8K*8. My TRS-80 model I, Basic level I came with only 4K*8 DRAM, but we could upgrade it ourselves using 16K*1 DRAM's to 16K*8 DRAM. The Level I Basic version had a 4K*8 ROM with a very primitive Basic in it. Tandy/RadioShack would upgrade that to Level 2 (Microsoft) Basic which had three ROM's for a total of 12K*8 ROM. The video would use another 1K*8 of the memory space and the keyboard would also use another 1K*8 so that left 2K*8 in the first 16K*8. I don't remember if that was being used for other IO or left unused. To fill the second halve of the memory with DRAM you would have to buy the expansion system, which could contain 16 pieces of 16K*1 DRAM's for a total of 32K*8 DRAM. The expansion system also added interfaces for a printer, floppy drives etc. It was a nice system and it used standard industrial busses, so you could easily attach standard floppy drives and printers etc. It was also all very well documented in books you could buy in the Tandy stores for very little. (The Radio Shack stores were called Tandy here in Europe.) One of the disadvantages was that during tape operation the clock interrupts were disabled, because they would interfere with the CPU-polled tape write and read timing. The system also didn't contain a DMA controller and the CPU, a Z80 at about 7.5 MHz was too slow to handle double density drives, so you could only use your expensive drives and floppies (a 5.25 inch floppy used to cost about $4) at half their capacity. Those were the days... ;-) Greetings, Jaap -- Author: Jaap van Ganswijk INET: [EMAIL PROTECTED] Fat City Network Services -- 858-538-5051 http://www.fatcity.com San Diego, California -- Mailing list and web hosting services --------------------------------------------------------------------- To REMOVE yourself from this mailing list, send an E-Mail message to: [EMAIL PROTECTED] (note EXACT spelling of 'ListGuru') and in the message BODY, include a line containing: UNSUB CHIPDIR-L (or the name of mailing list you want to be removed from). You may also send the HELP command for other information (like subscribing).
