IMSAI - SIO Board
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
Other IMSAI S-100 Boards
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