borriell@aecom.yu.edu (Frank Borriello) (06/26/90)
Although this may be redundant, I think it is worth warning anyone contemplating purchase of the NEC LC890 LED printer for use as a serial PostScript printer, that a serious design flaw makes this machine less than desirable. Although advertised as an RS-232 standard device, this is absolutely not the case. In fact it is a TTL port where the signals vary from 0 to +5V and not -6V to +6V as RS-232 stipulates. This is no small point since if you use a computer which expects to see RS-232 (notably SUN!) the printer will be invisible and not flow control signals will be perceived. At first I thought there was something wrong with either the printer or my SparcStation 1+ serial port. Checking with test equipment showed that the printer port was weird. A call to NEC which took the better part of an hour to connect to someone who even knew what a serial port was, confirmed that this is indeed a design "error" (my adjective not his) and that the solution was to use the centronics parallel port with a serial converter on the line. Besides the added cost of such a beast, this is unacceptable because the NEC parallel port is receive only so that queries to the postscript interpreter are lost and any software used which needs this feedback is negated. On many computers, this is not a problem since the ports are not sensitive to the voltage differences and thus will work fine (i.e. I used a UNIX PC for years without perceiveing the defect). However, as the relatively smug tech at SUN pointed out, when you use a high quality machine like SUN (his adjective not mine) which adheres to open computing standards like RS-232, then you must use high quality peripherals. Although I am kludging with the $90 converter, I think that NEC should have done something to make the machine do what it was sold to do - communicate with an RS-232 device! Their attitude showed me that NEC has no interest in end users and little pride in the quality of thier product or their public image. I therefore can only warn users of SUN equipment that NEC laserprinters may not be compatible with thier ports! ksk@kaecom.aecom.yu.edu
hess@IUVAX.CS.INDIANA.EDU (Caleb Hess) (07/12/90)
In article <9007120321.AA28460@crayola.cs.UMD.EDU> borriell@aecom.yu.edu (Frank Borriello) writes: >absolutely not the case. In fact it is a TTL port where the signals >vary from 0 to +5V and not -6V to +6V as RS-232 stipulates. This is no ^^^^^^^^^^ The last time I looked at the EIA RS-232 spec, it gave a range of -3V to -20something and +3V to +20something. I have run into a similar problem with a QMS-PS800 over a long wire run (about 200') where the voltage drop on the wire was enough to bring the voltage at the receiver down close to the threshold. The QMS is now working just fine with a short RS-232 cable. There is nothing wrong with using +/- 5V. for RS-232 drivers if you abide by the cable length recommendations. However, if your posting is correct and the printer port is not producing a negative voltage, then there is something wrong with the printer port - maybe a blown driver chip, or maybe the -5V supply has failed. I find it hard to believe that a manufacturer like NEC would deliberately design an RS-232 port without a negative voltage source.
shwake@raysnec.UUCP (Ray Shwake) (07/13/90)
In article <9007120321.AA28460@crayola.cs.UMD.EDU> borriell@aecom.yu.edu (Frank Borriello) writes: > >$90 converter, I think that NEC should have done something to make the >machine do what it was sold to do - communicate with an RS-232 device! Their >attitude showed me that NEC has no interest in end users and little pride in >the quality of thier product or their public image. I therefore can only >warn users of SUN equipment that NEC laserprinters may not be compatible >with thier ports! While our NEC laser printers haven't exhibited the serial interface problem you described, we have experienced numerous hardware (reliability) problems. I think we've got two or three of them in the storeroom awaiting repair. We've also had experience with NEC's Powermate 386 series. We waited months for their 3-1/2" floppy drive. Unavailable. Since NEC uses non-standard mounting rails, alternative drives won't fit - unless one can find NEC rails! We're also paying the price for their restrictive - and very proprietary - memory architecture.
fyl@ssc.UUCP (Phil Hughes) (07/17/90)
In article <50647@iuvax.cs.indiana.edu>, hess@IUVAX.CS.INDIANA.EDU (Caleb Hess) writes: > In article <9007120321.AA28460@crayola.cs.UMD.EDU> borriell@aecom.yu.edu (Frank Borriello) writes: > >absolutely not the case. In fact it is a TTL port where the signals > >vary from 0 to +5V and not -6V to +6V as RS-232 stipulates. This is no > ^^^^^^^^^^ > The last time I looked at the EIA RS-232 spec, it gave a range of > -3V to -20something and +3V to +20something. I have run into a similar > problem with a QMS-PS800 over a long wire run (about 200') where the > voltage drop on the wire was enough to bring the voltage at the receiver > down close to the threshold. The QMS is now working just fine with a > short RS-232 cable. There is nothing wrong with using +/- 5V. for RS-232 > drivers if you abide by the cable length recommendations. From my handy-dandy RS-232 Reference Card (which I wrote :-) ) the specs are >+3V for space, <-3V for mark. This are the required voltage levels at the receiver end. The Maximum open circuit voltage is 25V. One other characteristic that limits the cable length (and can be somewhat corrected by higher driving voltages) is that the maximum transition time is 4% of the bit time. The line capacity (which is also limited by the 2500pf maximum in the spec) is what slows down the transition. Transition time is defined as the amount of time the signal is between -3V and +3V. If the drivers are designed in a decent fashion you can send data really fast over moderate length cables. When manufacturers skimp you get into problems. The most common is those that don't have a -12V supply so they run the drivers off a -5V supply. This ends up giving you only a volt or so to play with to cover line drop. -- Phil Hughes, SSC, Inc. P.O. Box 55549, Seattle, WA 98155 (206)FOR-UNIX uunet!pilchuck!ssc!fyl or attmail!ssc!fyl (206)527-3385
shiva@well.UUCP (Kenneth Porter) (07/19/90)
Frank Borriello writes: > If you use a computer which expects to see RS-232 (notably > SUN!) the [LC890] printer will be invisible and no flow > control signals will be perceived. [The NEC LC890 RS-232 port > is] in fact ... a TTL port where the signals vary from 0 to +5V > and not -6V to +6V as RS-232 stipulates. I use an LC890 connected to my Sun 386i serial port with no problems. I haven't taken a DVM to the connector to see what the levels are, but my breakout box with two-color LEDS turns both red and green, suggesting both positive- and negative-going signals. I run the printer at 19200 baud, xon/xoff, and only occasionally hang the Sun serial port if my workstation gets too busy and drops an xon from the printer (the lpd daemon goes into infinite input wait waiting for the printer to send the xon and I have to reboot to clear the condition). I expect that if I were willing to put up with 9600 baud (Sun's official rating for the port), there would be no I/O errors at all. I did have trouble trying to run the printer in DTR/DSR mode (cross-wiring DTR to the Sun's CTS and DSR to RTS), but this didn't appear to work, and I've seen comments that RTS/CTS is only supported in one direction on Suns so I assumed that was the source of the problem. Ken (shiva@well.sf.ca.us)