Parallel Port
PSI BOX Reference
When used as an input, it can receive the output from a
computers parallel printer port and so act as the input for a
parallel to RS232 or parallel to IEEE interface.
When used an an output, the Centronics Parallel port is
normally used to drive a parallel printer.
Figure 4-2. Setting Parallel Port Direction.
_____________________________________
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6 Centronic O/P
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off
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DIP 6
PORT DIRECTION CHOSEN.
_____
______________________
0=Off
Centronics Port INPUT.
1=On
Centronics Port OUTPUT.
The Centronics Output Handshake.
_______________________________
The Centronics port output handshake is as follows.
A)
If the Centronics printer is busy, it should raise the BUSY
line true. The PSI BOX will not send any data out of the
Centronics port if the BUSY INPUT is high.
B)
When the BUSY INPUT line to the PSI BOX is low then
the PSI BOX will send any data in its buffer to the
Centronics port.
The PSI BOX places the first byte on the DATA 0-7 lines.
The PSI BOX allows the data lines to stabilise.
C)
Then the PSI BOX toggles the STROBE line low, for a
minimum of 1 microsecond. The Centr o/p LED flashes.
D)
The printer will respond by setting the BUSY line true,
high, and will read the data off the data bus.
Chapter 4
Page 33
