What is it?

A modern version of the MITS 88-2SIO Rev 0 Serial I/O Board used in the ALTAIR 8800 and other S-100 computers. This board provides one or two serial ports using the 68B50 ACIA.This board is functionally equivalent to the original MITS 88-2SIO Rev 0 board but is much easier to configure with switches instead of wire jumpers, supports baud rates up to 76.8K (great for the Serial Drive Server version of CP/M), has standard DTK/Intel/Crossed RS-232 10-pin IDC headers configured for DTE and DCE, and TXD and RXD status LEDs.

The 68B50 ACIA on the MITS 88-2SIO will not transmit or receive if CTS and DCD are not active. This Rev 1 board has switches that will pull these signals to ground if TXD and RXD are the only signals required.

The 68B50 does not provide for DTR. This Rev 1 board has a switch that will mirror RTS to the DTR pin.

This is for a bare board only.

Why get an 88-2SIO?

The MITS 88-2SIO is supported by all of the early software for the ALTAIR 8800, including original Altair BASIC written by Microsoft. If you want to relive the early days of S-100 computing, having an 88-2SIO board is a must.

Why did you make it?

I wanted a MITS 88-2SIO configured with switches instead of wire jumpers and the ability to connect standard IDC-10 to DE9 RS-232 cables. I also wanted faster data rates for Serial CP/M and data transfers.

What makes it special?

This is the first board I designed from scratch.

No Warranty

This board was designed by a hobbyist for fun and is not a commercial product. This board and components come with no warranty.