Author Topic: LPT1 settings  (Read 20150 times)


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LPT1 settings
« on: November 11, 2011, 11:39:04 am »
I am trying to get my WQindows XP machines (ECP or EPP) LPT1 port to behave like the older SPP port. SPP supported out 956,255 and out 956,0 to toggle pins 2-9 on the DB25 port from steady high to steady low. The newer ECP and EPP seem to toggle high for 50 nanosecs, or so, and revert back to low--0 volts out. I have a quadrature application that requires the use of the SPP style of "outing and holding" poked values. Any thoughts? I have ordered another of Jan's books and hope to find the answer there. Something about base address plus 400h.

Jan Axelson

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Re: LPT1 settings
« Reply #1 on: November 11, 2011, 12:29:07 pm »
Try setting the port to SPP or PS/2 mode in the system BIOS.

Configure the data lines as outputs by writing zero to bit 5 of the control port (base address + 2).

Also see this question:

If a logic 1 is written to the Control Port, bit 0, (Strobe), the PC clears all of the port bits once every five seconds for about a minute.

« Last Edit: June 29, 2015, 10:20:28 am by Jan Axelson »