PARALLEL.TXT

BenOS v1.0 parallel port driver (c) Benjamin Hoyt 1998

This parallel port driver has a queue or buffer which user data is
stored in before being sent to the parallel port. A background task
actually sends the data. If the buffer is full when the user tries
to send data he is given an I/O result of -275. lpt-emit and lpt-type
are user words for sending data to the parallel port.

The data output port (which is readable) bits 0-7 correspond directly
to the pins on the parallel port 2-9. Data written to this port goes
directly to the printer. The data port address is at lpt-port.

The status register port is a readable port which gives various
status information about the printer. The status port address is at
lpt-port + 1. The following is a description of each status bit:

bit#	description
----	-----------
0		set = time-out
1-2		unused
3		set = error (port pin 15)
4		set = printer on-line (port pin 13)
5		set = out of paper (port pin 12)
6		clear = acknowledge (port pin 10)
7		clear = busy (port pin 11)

The control register is a writable port which controls various
printer actions. The control port address is at lpt-port + 2. The
following is a description of each control bit:

bit#	description
----	-----------
0		set = output data to printer (port pin 1)
1		set = auto line feed (port pin 14)
2		clear = initialise printer (port pin 16)
3		set = printer reads output (port pin 17)
4		set = enable IRQ for acknowledge
5-7		unused