benson@rlgvax.UUCP (Paul Benson) (09/07/89)
+++++++++++++++++++++++++ INFORMATION PLEASE +++++++++++++++++++++++++ Need a few things cleared up about PC parallel ports (parallel port on AT I/O card only). Apparently, there are problems with parallel ports: 1. interrupt not latched? does this really matter? If it does, does an IO card manufacturer produce one that is latched? Are there work arounds for missed interrupts? will the 8259 go into an error condition if it sees the parallel port drop the request? (thus getting interupt anyway without being latched, or setting interrupt pending?) 2. 8259 will generate an IRQ7 as an error condition occurs, how does one detect that this is the case instead of the parallel port generating it? (besides just using IRQ5, some IO Cards don't give a choice of interupts (some don't do ints at all)) 3. Some cards generate IRQ as the printer asserts NOT BUSY, while others use other signals, does anyone know of a card that uses ACKnowlege for the IRQ? This because some printers do not (or optionally will not ) assert NOT BUSY before ACK!?!?! (info please) 4. Many printers use the status port (tied directly to their status pins) in a non-standard fashion, does anyone what the standard is? and does any know if at least the error bit is same for all printers? 5. Timeouts -- Why does the port half to hang out at all, why doesn't the printer ack or set error bit immediatly? Is there a GOOD reason for the occasional abnormally long period of time before the printer ACK's? do printers normally print or complete control sequence before ACKing? what is going on? Any help on these matters is greatly appreciated!! Posted By Bob Thralls ICL North America, Business Systems (was CCI)