B&B Electronics Parallel Port Input/Output Converter PPIO - Manual (Page 6)

4 PPIO2899 Manual
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used to read the status of the port. The PPIO does not need to use
this port as an input port.
Again, referring to Table 1, if you input the data on port
0379H, then whatever TTL level pins 15, 13, 12, 10, and 11 are will
show up as bits 3 through 7. The state of bits 0, 1, and 2 will be
unknown since they are not hooked to anything, but they probably
will be HIGH (ONE). Note that the data on pin 11 will be inverted, if
pin 11 is LOW you will get a HIGH on bit 7. The pins with the “bars”
over them are all inverted. This is done by the hardware in the
parallel port over which we have no control. A way to read these pins
using GWBASIC is: A1=INP(&H379). A1 will then have the results of
the input from port address 0379H. Bit 3 of A1 will have the status of
pin 15, bit 4 the status of pin 13, etc.
Note that on the third address (037AH) the pins can be
either inputs or outputs. If you use the GWBASIC command OUT
&H37A,&H01 (00000001 BINARY) then pin 1 will be LOW (because
it is inverted), pins 14 and 17 will be HIGH (they also are inverted),
and pin 16 will be LOW (it is not inverted).