On 12/3/2014 12:12 AM, Eric Smith wrote: That would be a fun and worthwhile project; I wish I had more information about the MX-30 RAM and how it's different. Infotek basically replaced every HP component (except the backplane) with the MX-30, so it could be radically different than the original. The HP Museum has some pretty good pictures, see here: http://www.hpmuseum.net/exhibit.php?hwimg=1060. If you need something more detailed, let me know and I can run them through my scanner (not the feeder portion). - Josh

On 2014-Dec-03, at 12:12 AM, Eric Smith wrote: Would this be for the sake of a fun project, or would it be practical necessity, such as need & availability of 1103's for repair?

You can, of course, pick up the M register (memory address) on the top test connector of the memory address PCB. One gotcha, which I am sure you are aware of. The 98x0 do not have a nice, simple ROM/RAM address map. Most of the lower part of the address space is ROM, but there is a 512W (IIRC) block of RAM near the start where the processor stores the stack pointer, floating point registers, etc. It's something of a kludge, but the addresses had to be picked to take as few microinstructions as possible to generate (which means blocks of contiguous 1s and 0s in the address). The address decoding in a stock machine is done on the memory address PCB which outputs a select line for each 1KW block (== each bank of 1103s, of course). So you would either have to use that (at least for the first 1KW of RAM) or pick up all the address lines after M(9) (bits 0 to 9 are on the memory slot connector) and re-implement the address decoder. Not at all difficult, but something to realise before you start wiring up ICs... I assume you're jsut going to be plugging into the HP9830 I/O slot and not tryign to share between 4 machines. Or indeed using a mechanical disk drive. It shouldn't be too hard. The interface is basically programmed I/O for the commands (2 bytes, one is basically cylinder, the other is sector and read/write control). One of the status lines is the command byte selector, another 2 select the disk (not strictly the drive, an HP7900 is treated as 2 disks here). And what HP called DMA and the rest of the world call memory mapped I/O for a 256 word sector buffer. There's a fair amount of logic in a real 9880 system that you could forget about. Things like the actual width of the sector buffer -- it's 4 bits wide in the hardware. So much of the logic in the 11273 'cable' is involved with doing the transfer (bit serial of course) to/from the 9830 a nybble at a time. Then the disk data shift registers are 8 bits, so there's more buffers and latches to convert between that and the 4 bit buffer RAM. I have a real HP9880 going on the bench when I have finally sorted everythign out here. Well, OK, the drive is a 7900A taken from my 2100A system, it doesn't have the tabletop case of a 9880, but electronically it's all the right stuff, it's all HP. Getting that all going will be a fun project. -tony

I don't really see the point. It's fairly easy to make a ROM cartridge that takes EPROMS (IIRC 2 EPROMs, a 74x00 and a couple of transistors (to convert the 12V selects back to 5V). Such a board (hand wired) was shown at HPCC a couple of years ago. If you do make your own Mass Memory ROM module, figure out a way to have a switch to disable it. The Mass Memory ROM intercepts all sorts of BASIC commands, to the extent that DISP and PRINT (at least) fail unless there is a working disk drive connected too. Continually plugging and unplugging the ROM is hard on the connectors (yes, you can still get them, but desoldering the old one is a pain). Incidentally, the ROM module connector on the 9830 (but not on the smaller machines) is 0.125" pitch, double sides, 18 pins on each side. Now where have you seen that before :-). It made finding an extender board very easy when I was fiddling in that area. -tony

On Fri, Dec 5, 2014 at 11:26 AM, tony duell <ard at p850ug1.demon.co.uk> wrote: Since there has to be memory-mapped RAM on the board anyhow, it's trivial to also have the ROM. It also adds zero components to my design.

On Fri, Dec 5, 2014 at 12:50 AM, Brent Hilpert <hilpert at cs.ubc.ca> wrote: Thanks for the offer. I've got four tubes of 1103A chips that are actually surplus from HP. I haven't tested any yet, but I expect that they should be OK. A friend has a MIL8008. Before he showed me that I wasn't aware that there had been a second source for the 8008.