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Vector ZCB Single Board Computer
2.4.3 Asynchronous serial baud rate selection
You select the desired baud rate through a combination of hardware
switches and software.
If
you are using the standard operating systems and
Extended Systems Monitors for Vector Graphic Systems, however, you need only
be concerned with the hardware switches.
The hardware switch is located in the upper left hand corner of the
board.
It is labeled "Baud Rate Select
It •
The switch contains eight rockers
labeled
"III
to "8" and also labeled 119600,11 "4800,11 "2400,11 "1200,11 11600,11
11300,11 11150," and 11110. 11
The switch is, in addition, labeled 1I0PEN
II
on the
left side.
To
select one of the labeled baud rates, press the desired rocker down on
the right side, Le. on the side opposite the 1I0PEN" designation.
Then
press all other rockers down on the left side, i. e. toward the "OPEN"
designation.
The result must be that one-rocker is down toward the right,
and all others are down toward the left.
Otherwise none of the serial
channels will not w::>rk at all.
If you are not using the serial channel, switch them to the "OPEN"
position.
The labeled baud rates assume that the corresponding 8251 will be
initialized for a clock factor of 16.
(It creates the baud rate by dividing
the clock input by 16.)
This initialization is handled in software, as
described in the 8251 references given in Perspective.
All standard vector
Graphic software, unless otherwise documented, use a clock factor of 16, and
therefore the labeled baud rates are correct.
However, custom software can use a clock factor of 64.
If this is the
case, the actual baud rate will be 1/4 of the baud rate selected on the
switch.
(The only two asynchronous clock factors allowed by the 8251' s are
16 and 64.)
Further, it may be desired to create software which allows the
operator to choose between two baud rates that differ by a factor of 4.
For
example, the software may be designed in conjunction with a modem that can
accept signals at either 300 or 1200 baud.
In
this case, you would create
the software so that the operator
I
s input determines whether the 8251 is
initialized with a clock rate factor of 64 or 16, respectively.
Remember,
if
you are using standard Vector Graphic software, do not worry
about this software option.
You simply set the baud rate for a desired
serial channel by setting the baud rate select swi tch on the ZCB
II
board.
2.4.4 How to connect most
RS-232C
serial terminals and printers
To connect the serial channel to an external peripheral, plug the male
16-pin connector of the ZCB serial I/O cable into the 16-pin socket of the
desired serial channel, on the upper right side of the ooard.
Then, in
most cases connect the DB-25 socket at the end of this cable to the
peripheral, using a 25-wire flat ribbon cable.
cetails (and exceptions) are
as follows:
Rev.
I-B
6/11/80
2-11
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