This is the reproduction of the Altair 680B Main Board.
The changes from the original PC were minor; a few extra pads were added to allow easier installation of today's smaller crystals plus a couple of additional capacitor mounting pads.
The Altair in its basic form could not run BASIC or a disk operating system. An optional language called VLT2 was available. Installing VLT2 took 3 1702s; the fourth 1702 was used for the machine language monitor included with the main board. Microsoft Basic required the addition of a 16K memory board. With use of the MIO board it is possible to run FLEX.
When building the reproduction main board please use the parts list in the Peripheral Technology manual. The use of the parts listed in the manual results in an improved board. The main difference is the recommendation to use a DC-DC converter instead of a 7805 and some of the capacitor values have been changed. While you may certainly build the reproduction using the MITS parts list, your board will suffer with the same problems that affected Altair's of the day.
2MHZ Main Board - Configurable for 500KHZ, 1 MHZ and 2 MHZ
The 2 MHZ main board is very similar to our reproduction main board. CPU speed selection is by jumpers. Speed can be configured for 500KHZ, 1MHZ or 2MHZ. There is also a jumper to disable the onboard 1K RAM. The 2MHZ main board has thin traces connecting the usual choice of configuration jumpers. The board is configured for RAM at address 0000, baud rate set to 9600 and the terminal type is set for RS232. Should you wish different choices, the traces are very thin and easy to cut. You can then solder jumper wires in place like the original main board.
To take advantage of the 2MHZ speed you will need to pair this main board with the Peripheral Technology MIO board. The onboard 2102 RAM and 1702 EPROMS are simply not fast enough for 2MHZ operation.
Here is a close up of the configuration section.
Downloads
Manuals:
PT680Main.pdf Peripheral Technology Main Board Reproduction Manual
These are MITS Altair manuals. Please read the Peripheral Technology manual first. Some part types and values have been changed.
680 Assembly Manual.pdf Altair Assembly Manual
Altair 680b Operators_Manual.pdf Altair 680 Users Manual
680 Theory of Operation.pdf Altair 680 Theory of Operation
Altair 680b Monitor Manual.pdf Altair Monitor Manual
Altair 680b BASIC Manual.pdf Altair Basic Manual
At present we cannot program 1702's. The assembled Main Board ships without RAM or EPROM. It will be necessary to use the MIO board for RAM and EPROM
| Altair-Main-Bare | Bare Reproduction Altair Main Board | $39 |
| Altair-Main-ASM | Assembled and Tested Altair Main board - does ship with RAM or EPROM | $209 |
| Altair-Main-2MHZ-Bare | Bare Reproduction Altair Main Board updated for 2MHZ operation | $39 |
| Altair-Main-2MHZ-ASM | Assembled/Tested 2MHZ Altair main board - does not ship with RAM or EPROM | $215 |
| Altair-Main-1K | 1K RAM, 8 2102, For Main Board - not needed if using MIO board | $29 |