Processor Technology - 3P+S I/O Board
This was a very flexible and popular Processor Technology board.  It was utilized in many early S-100 systems.

The 3P+S Input/Output S-100 board was designed to meet all the I/O needs of most early 8800 system users.  For example, one teletype and two TV typewriters with keyboards could be operate simultaneously with the 8800 through only one 3P+S.  Similarly, one RS-232-C modem, a teletype, and one TV typewriter plus another parallel data device could all be interfaced with one 3P+S at the same time.
 
One parallel port was available to set up control conditions for both parallel and serial ports, as well as to set the serial I/O baud rate under program control.  The baud rate could be set from 35 to 9600 Baud.  Another parallel port allowed polling the input data available flags and external device ready flags.  This port also permitted checking the serial I/O error flags.  Full handshaking with both input and output peripherals could be implemented. 
 
Module addressing was jumper selectable to any one of 64 I/O ports within the 8800 range of 256 I/O ports.  Additional flexibility allowed either the UART (Universal Asynchronous Receiver Transmitter) and control port or the two parallel ports to occupy the lower two relative addresses. Interfacing to the 8800 vectored interrupt bus was provided as a jumper selectable option.  Any of the UART error flags or hand­shaking signals could be used to generate interrupts.  A Vectored Interrupt Module, however, was required for this purpose. 
 
The manual for this board can be obtained here.  Click here to see an early review of this board that appeared in the October 1976 issue of Popular Electronics.  Click here to see an early review of the CUTS tape standard that appeared in the March1976 issue of Popular Electronics.