Getting as much speed out of the "Serial Bus” between your Altair and your PC is important. Here is a simple modification to the standard MITS 88-2SIO card that will provide operation at 19,200 baud – twice that of the “fastest” 9600 baud listed.
On the back of the card add a wire from IC G, pin3 to what would be pin 16 of an IC socket (or simply the available plated through hole in that location.) This provides the required clock signal for use by the M6850 UART chips.
On the front of the card you can see I have installed a 16 pin IC socket. The new 19,200 baud clock rate is now available in the upper right corner, pin 16.
