heff@flnexus.ATT.COM (Paul_Heffner) (02/07/89)
From article <1688@lamc.UUCP>, by info-3b2@lamc.UUCP (Info-3b2 Mailer): > Info-3b2 Digest, Number 56 >We recently moved a HP laserjet+ printer from a 3B2 PORTS card to an EPORTS >card. Running off the EPORTS card is generating a high number of >error 22s from the laserjet. We are using the standard black modular cable >and the terminal/printer connector. Do the EPORTS card require a different >type of modular connector? > First, unless the HP needs to indicate "potential overrun" by dropping > an interface tag (DTR) and re-activate this line when the condition > has passed I'd say the standard "black cable" and Terminal/printer > adapter will suffice. *In which case XON/XOFF is normally employed. If > hardware signals (either DTR or CTS) are needed to "throttle" data > transmission then clearly the Terminal/Printer connector and various > EPORTS, HP and LP Spooler options need to be reconsidered. In a nutshell the Terminal/Printer adapter will either need to be rewired or the correct one I'm not aware if the electrical interface is the same on the Laserjet+ and the Laserjet II models, but I just fixed this problem on our Laserjet II after a lot of fooling around with a breakout box and a Data Line Monitor. Quoting from the "Getting Started with the Laserjet Series II Printer" manual: (pg. 3-74) ========== Signal Protocol The signal protocols supported by the Laserjet series II printer are X-ON/X-OFF and DTR. The Printer does not support Enquire/Acknowledge.... ========== They're not kidding. When the buffer is getting full the printer sends a DC3 (X-OFF) *and* DROPS DTR (line 20). Conversely, the damn thing holds line 4 (CTS) steady instead of toggling it. Additionally, the printer uses something they refer to as "Robust X-ON/X-OFF", which means that it belches DC1 characters at the host every couple of seconds. The EPORTS board has hardware flow control implemented through the CTS/RTS lines if you enable it with the epstty(1) command, but the X-ON/X-OFF is sufficient for our purposes. The fix was to make a custom modular plug. The usual wiring of a Terminal/Printer plug is: Terminal/Printer plug wiring: RJ-45 DB-25 Color ===== ===== ===== 1 5 Slate (Grey) 2 7 Brown 3 6 & 20 Yellow 4 2 Green 5 8 Red 6 3 Black 7 4 Orange 8 1 Blue My "fix" plug looks like: RJ-45 DB-25 Color ===== ===== ===== 1 5 Slate (Grey) 2 7 Brown 3 4 Yellow 4 2 Green 5 6 Red 6 3 Black 7 20 Orange 8 1 Blue By catching DTR off line 4 (ordinarily CTS) which the LJ holds steady, and sending line 20 (ordinarily DTR, but toggled by the LJ for flow control..) to the control-in of the EPORTS board, you can use X-ON/X-OFF flow control by having "stty ixon -ixany" in the interface script for your printer or use the epstty command to use the hardware handshaking. Heff