B&B Electronics PPIO manual Bit

	378H		379H		37AH
BIT	Output	Input	Output	Input	Output	Input
					_	_
0	2	2	X	X	1	1
					_	_
1	3	3	X	X	14	14
2	4	4	X	X	16	16
					_	_
3	5	5	X	15	17	17
					See	See
4	6	6	X	13	Note 2	Note 2
5	7	7	X	12	X	X
6	8	8	X	10	X	X
				_
7	9	9	X	11	X	X

Table 1

Note 1: X means no connection to any DB-25 pin.

Note 2: Bit 4 of 37AH as an output is used to control the interrupt IRQ7. When this bit is HIGH, IRQ7 is enabled and when this bit is LOW, IRQ7 is disabled. As an input, this reads the status of the IRQ7 interrupt to see if it is enabled or not.

Note 3: The “bars” over the top of some pin numbers indicate that those signals are inverted (in hardware) from PC's bus to DB-25 pin.

You can also read pins 1, 14, 16, and 17 using the INP(&H37A) command. For this to work properly, you must first force all the outputs HIGH. The way the parallel port is wired, if you do not force the outputs HIGH they will interfere with the inputs. To do this, use the command OUT &H37A,&H04 (04H is the same as 00000100 binary). Pins 1, 14, and 17 are inverting so a ZERO written to them forces them HIGH. Pin 16 is non-inverting so the ONE written to it forces it HIGH. After issuing the OUT command you can then do a A2=INP(&H37A) that will read the TTL levels on those pins. In this case the four upper bits (bits 4-7) will be unknown, but will probably be HIGH.

PPIO2899 Manual 5

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