SWTPC 6800

Another old interesting computer, at least it's interesting to me. When I worked at a small Newspaper communications company in NJ (1985) I had the fortune to work with a SWTPC 6800 (dual 8" drives and I think a single 5 1/4" drive). We used this system as part of our development systems (done in assembly language)

So what did I end up with. Well a decent vintage machine. First, it appears it is pretty clean. Not a lot of dust on it. I didn't get an disk systems with the machine, but that's okay. I can make it work without the disks. I'll explain that voodoo later. Cool part is that they knew about this method back when these machines were new. It just wasn't very practical at the time (client/server setup).

• MP-F case
• MP-B Motherboard
• 16K SRAM board
• 64K SRAM board (6116 x17)
• 32K ROM board (x6 top, x8 bottom, most likely 2716s)
• MP-A2 (4 2716 ROMs - 8K, 1 6810)
• Smoke Signal Broadcast BFD-68A
• MP-C (set up for cassette)
• MP-S - serial interface
• MP-LA -
• MP-LA
• Custom ACIA proto board (MP-S like) (console?)
• MP-R EPROM Programmer

MP-B Mother Board

MP-B2 Mother Board

The MP-B2 Mother Board is a 9 " x 14" double sided plated thru hole board onto which all of the various processor boards are plugged. Provisions have been made for one processor board, up to four memory boards plus two unused slots. This gives the user the ability to handle up to 32K words of memory. The mother board also provides the line buffering and address decoding for up to eight interface boards. Although one of the eight must be the serial control interface, the other seven may be any combination of serial (MP-S) and parallel (MP-L) interfaces the user may choose to have.

SS50 (x7) and SS30 (x8) slots.

From the Assembly Instructions:

The original MP-B Mother Board decoded the entire 8 K block of memory from 32K thru 40K as being resident on the mother board. Although simpler from a circuitry viewpoint, this technique was wasteful and has been changed on this version, the MP-B2, so that only the 32K thru 36K block has been allocated to the mother board interface addresses. This allows boards outside the interface address range to use the 36K thru 40K memory addresses. The new decoding arrangement also makes it easy to reassign the interface address block to any 4K region from 32K to 64K in 4K increments. Although this isn't allowable when using the MIKBUG® or SWTBUG® monitors, it does have potential when using custom monitors.

Missing aluminum trim

A quick note, I (Neil Cherry) didn't do this. Mike Douglas (DeRamp) did and I copied it here for reference. Attribution: MP_F.htm

A "feature" of the SWTPC was the perforated metal cover with aluminum trim. You had to remove 14 screws to get the cover off. People ran the computer with the lid off or just placed on the case. Often when the SWTPC 6800 comes up for auction on eBay it is missing the aluminum trim.

The aluminum trim is easy to replace. You can get the 1/16 inch thick 3/4 inch x 1/2 inch unequal angle at a hardware store. It cost around 3 or 4 dollars for a 36 inch length. The screw are 6-32 3/8 inch truss head screws. I found them in a specialty fastener store.

Mike Douglas received a SWTPC 6800 without the cover and wondered what to do with it. Earlier Mike had determined what type a aluminum was used for the cover. Mike had been thinking a modifying a new PC case to look like a SWTPC so Mike ordered a sheet of perforated aluminum. The material is 1/8 inch round hole, 3/16 inch center, 60 degree angle, 0.063 inch thick 3003H14 perforated aluminum. Mike got a 36 by 96 inch sheet from McNichols Co. for $120. That is enough for 6 cases, but they do sell smaller amounts. (This is not going to be a cheap project.)

Pictures