EPORTS to the Laserjet

[Paul_Heffner]

>From article <1688 at lamc.UUCP>, by info-3b2 at 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