jwaas.es@PARC-MAXC.ARPA (02/09/84)
The IBM PC running CPM with the parallel printer port assigned as the list device does not conform to the Centronics protocal. Apparently there is some intervening interrupt which causes the driver routine to fail to always find the BUSY term from the printer. This in turn causes the IBM to assume that since it could not find BUSY it of course is in fact busy ( go ahead reread what I just wrote ). The driver therefore must first find BUSY then determine that it has gone away. In any event to insure that BUSY is found the term must be held for around 450 milliseconds which is several hunderd more than Centronics. The EPSON printer appears to work well with the IBM with a BUSY of 65 milliseconds but in fact does occasionaly hang up as Busy when it is not. Investigation showed that even a couple of milliseconds plus or minus of 65 results in considerable failures. At around 25 milliseconds the IBM refuses to run., It would appear that EPSON just happens to synchronize with the possible intervening interrupt most of the time. MSDOS runs with Centronics protocall (or was that PC DOS or both). Jaye