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This was IMSAI's initial and main S-100 board for RS232 serial IO. It was quite popular and easy to program although it did utilize a block of 16 I/O ports.


The IMSAI SIO Board provided a serial input/output capability for the IMSAI 8080 System.     It contained  two serial I/O ports, providing  two complete  RS232  full duplex data  lines with all control signals.     Data lines for both channels were provided in RS232, TTL Level and current loop formats. Asynchronous or synchronous  lines utilizing full or half duplex could be  run with this board at any rate up to 9600 baud in the Asynchronous mode and 56,000 baud in the Synchronous mode. The  SIO  Board could be  jumper-selected  to  respond  either to input and output instructions from the IMSAI 8080 System or to memory reference instructions for  memory-mapped  I/O.
Operation of  the board  requires  16 I/O  port  or address locations, which are  selected by address bits 0  through 3.    When the board is used with  input and output instructions,   address bits 4  through 7 form  the   remainder of  the board  address   and are   jumper  selectable.     When  the board is used as memory-mapped I/O,  the lower byte of address is  jumper  selected exactly  the  same  as  an   I/O  port address and the  upper byte of  address is hex FEH. 
The  SIO  Board  was  structured around a  pair of  Intel 8251 USART   (Universal  Synchronous-Asynchronous   Receiver-Transmitter)   devices. The  8251  chips  provided  for  extensive  program control  of the  input/output  functions  including  the  RS232  Control Line  and  sync  character selection  in  the  Synchronous  mode and error condition  sense  and  recovery.  The board provided interrupt generation for received characters,   empty transmitter buffers,   and sync characters  detected with provision for jumper selecting the priority of the   interrupt.     The interrupt can be made to work in conjunction with IMSAI's  Priority Interrupt/ Clock board  (PIC-8).  All functions may also be  program controlled so  that  the full capability of the board is available  to  the machine without the use of interrupts.    All RS232 level drivers and  receivers  necessary  for  two complete  RS232   lines  are included on  the board.   
The manual (updated) for this board can be obtained here and the schematic can be see here.


Other IMSAI S-100 Boards
4KRAM   8080CPU   EPROM-Programmer    MPU-B   PIC-8   PIO   PROM-4   SIO   VIO  MIO



This page was last modified on 10/25/2013