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FUNCTIONAL DESCRIPTION
The SIO Board provides a serial input/output capability
for the IMSAI 8080 System.
ports, providing two complete RS232 full duplex data lines
with all control signals.
are provided in RS 232, TTL Level and current loop formats.
Asynchronous or synchronous lines utilizing full or half
duplex can 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 may 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 i -s used with input and output instruc
tions, address bits . . 4 through 7 form the remainder of the
board address and are jumper selectable.
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 FE or octal 376.
The SIO Board is structured around a pair of Intel 8251
USART (Universal Synchronous-Asynchronous Receiver-
Transmitter) devices.
The 8251 chips provide 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.
interrupt generation for received characters, empty trans
mitter buffers, and sync characters detected with provision
for jumper selecting the priority of the interrupt.
interrupt works in conjunction with the 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.
and receivers necessary for two complete RS232 lines are
included on the board.
SIO 2 Board Rev. 3
Functional Description
Edition 2
SIO 2 Board
It contains two serial I/O
Data lines for both channels
All RS232 level drivers
When the board
The board provides
The
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