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3.3
SYNCHRONOUS OPERATION
North Star HSIO-4
Used primarily to facilitate rapid data
communication between two computers,
synchronous transmission is also used to
communicate with devices that are capable only
of synchronous operation, such as hign-speed
modems.
During synchronous operation, data
transmission is synchronized and controlled by
equally spaced clock signals. The clock signal
is generated by the transmitting port and then
used by the receiving port. The timing of the
clock signal (and speed at which the sending
port transmits data) is determined by the baud
rate setting for that port.
rate for both the transmitting port and the
receiving port is determined by the baud rate
selected at the transmitting end.
As supplied, all four HSIO-4 ports are
configured for asynchronous operation. Each
port can be reconfigured for synchronous
operation (see Sections 3.3.1. and 3.3.2).
Sections 3.3.3 and 3.3.5 provide examples of
how to program synchronous operation.
Each HSIO-4 port may be configured for
synchronous operation in one of two
possible ways:
FIXED BAUD RATE (55.8KHz)
The first method allows a synchronous port to
transmit at a single fixed baud rate of
55.8KHz, which is the maximum possible
synchronous speed provided on the HSIO-4. This
method requires two configuration changes,
which effect only the modified port.
PROGRAMMABLE BAUD RATES
The second method permits a synchronous port
to use any one of five programmable baud
rates ranging from 1.76KHZ to 38.4KHz. A
programmable 55.8KHZ baud rate is also
possible, but requires an additional jumper
change, which effects all four ports.
38
Thus, the baud
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