croehrig@audiolab.uwaterloo.ca () (09/08/90)
I am having problems wiring up an HP LaserJet III to the cube over the serial lines. Using a digital scope, I've determined that the problem is that the NeXT is taking too long (30-100 ms) to cease transmission after it gets an XOFF from the printer and the printer's input buffer overflows as a result (the HP says I/O CONFIG ERROR). This only happens at 19.2k and sometimes 9600 baud; at 4800 baud the printer can keep up with the transmission and no flow control is needed. The fact that the length of time varies leads me to believe that the XON/XOFF flow control is handled in software instead of by the Zilog 8530 Serial Communications Controller. Is there any reason for this? It doesn't make sense to have a fancy chip that doesn't handle flow control automatically. Has anyone else run into this problem? If flow control really is handled in software, is there any way to speed up the response to XON/XOFF (fix the ioctl routine or something)? 100 ms is a really long time for a routine to execute, even for a NeXT. Chris Roehrig Audio Research Group University of Waterloo. response time