Dual Systems -- SIO4 Serial I/O Board
The SI04-DMA was an intelligent, high performance,
four-port serial input/output board. It conformed to the IEEE-696/ S-100
specification but is also designed to work with older S-100 systems.
The board was intended to be used with asynchronous
terminals or printers in multi-user systems and had the necessary features
to work with modems. A limited synchronous mode capability added
All input data to the SI04-DMA passed through a 256-byte FIFO buffer,
removing the requirement for a fast response time from the operating system
and avoiding the possibility of "lost" characters. On output, the SI04-DMA
reads characters directly from the S-100 machine's memory via DMA
and transfers them to the serial port. This reduced the operating systems
overhead for output operations several hundred times. The board was capable
of a full 24-bit address range and incremented over any address boundary.
Baud rate was independently selectable on each channel by program. Sixteen
of the most popular speeds were provided.
The SI04-DMA was the first S-100 serial interface board designed
specifically to reduce operating system overhead in multi-user systems. The
tasks normally performed by the operating system to handle serial input and
output are assisted by intelligence built into the onboard microcomputer
(8085A) assisted S104.
Bus Compatibility: The SIO4-DMA was compatible with the
IEEE 696/ S-100 specifications as defined in January 1982 and was suitable
for systems with up to 8MHz clocks. The SI04-DMA was also intended lo be
compatible with many older S-100 computers.
IEEE 696/S-100 Compliance: M24, VI, TM, F8, W1-16. Number
of wait states depends on S-100 dock rate and state of SI04-DMA when
Address Selection: I/O address selected by DIP switch.
Eight bits of VO address are decoded.
Operating Power: The maximum power consumption is: +8
Volts® 1.3 Amps +16 Volts® 0.1 Amps -16 Volts ©0.1 Amps
RS-232 Compliance: All RS-232 drivers and receivers conform
to the RS-232 specification. The SI04-DMA can simulate either a modem (DCE)
or terminal (DTE) for connection to a terminal or modem respectively.
Synchronous Mode: In the synchronous mode the external clock signal
determines receive baud rate. A transmit clock is provided by the SI04-DMA
at the selected baud rate. Baud Rates:
Baud rates are available: 45.5.....9600.....3840.
I cannot locate a better image for this very useful board. Nor can I locate
If you would like to submit one or both please let me know.
There is a great write-up on this board in the March 1984 Microsystems
Journal (Vol 5, p103).
Other Dual Systems
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