B&B Electronics Parallel Port Input/Output Converter PPIO - Manual (Page 12)

10 PPIO2899 Manual
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Table 2
The big advantage of using the ANDing and ORing as shown in
Table 2 is that it makes each PPIO pin independent. If you have, for
instance, PPIO bit 2 ON and all of the rest of the bits OFF then your
variable OB will be equal to 04H (00000100 binary). PPIO bit 2 will
be LOW or ON. If you then want to turn ON bit 3 do the following:
500 OB=OB OR &H08
520 OUT &H378,OB
Bit 3 will go LOW and bit 2 will stay LOW. At that time OB will be
equal to &H0C (00001100 binary). To turn OFF bit 3 do the
following:
700 OB=OB AND NOT &H08
720 OUT &H378,OB
Bit 3 will go HIGH or open and bit 2 will stay LOW. By using the OR
and AND NOT commands in Table 2, bit 3 has been turned ON and
OFF without disturbing any of the other PPIO Bits.
You may also use the PPIO with some pins as inputs and some
pins as outputs. There can be any number of each and in any order.
Remember that before you can use a PPIO pin as an input you must
first force the output driver on that pin OFF by putting a ZERO on
that bit. For example suppose we want to use bits 0, 1, and 2 as
outputs and bits 3, 4, 5, 6, and 7 as inputs. We also want bit 1 to be
ON (or LOW) when we start the program. We need to turn OFF bits
3, 4, 5, 6, and 7 so we can use them as inputs and turn ON the
output bit 1. You should modify Figure 2 to add the following line:
180 OUT &H378,&H02
From then on you can use the first three lines of Table 2 to
control the three outputs and lines 220-320 of Figure 2 to input data.
I/O Bit Force I/O ON
(Low)
Force I/O OFF
(High)
0 OR &H01 AND NOT &H01
1 OR &H02 AND NOT &H02
2 OR &H04 AND NOT &H04
3 OR &H08 AND NOT &H08
4 OR &H10 AND NOT &H10
5 OR &H20 AND NOT &H20
6 OR &H40 AND NOT &H40
7 OR &H80 AND NOT &H80