rcd@cbnewsj.ATT.COM (rana.c.dutt) (03/21/90)
My brother just bought an HP Deskjet Plus for his ST. I remember people reporting power up problems that affect the ST's parallel port when this printer is attached. There seems to have been two kinds of problems: 1) the Deskjet Plus allegedly causing hardware damage to the ST's parallel port and 2) a problem that causes TOS not to print to the Deskjet if the wrong power up sequence is used. Problem 2) had to do with the STROBE line, and I have saved John Logajan's article detailing a PNP transistor attachment to fix it. Now, what was the conclusion to problem 1)? Is it true that if the DJ Plus is directly connected to the ST parallel port, damage can be done to the port? Thanks for any replies, and I'm sorry if this has come up before. Rana Dutt rcd@mtqua.att.com
logajan@ns.network.com (John Logajan) (03/22/90)
In article <4275@cbnewsj.ATT.COM> rcd@cbnewsj.ATT.COM (rana.c.dutt) writes: >Now, what was the conclusion to problem 1)? Is it true that if the DJ Plus >is directly connected to the ST parallel port, damage can be done to the >port? Thanks for any replies, and I'm sorry if this has come up before. I measured the voltage levels on the data lines cause by the 2000 ohm pull-up resistors in the HP DeskJet Plus. The low levels were under 3/10ths of a volt, well within the 8/10ths of a volt maximum-allowable standard TTL low level. (There is no maximum-allowable high voltage beyond the supply voltage of 5 volts to worry about -- the pull-up resistors will never pull it over 5 volts unless they decide to become electrical generators -- which would be bigger news than cold fusion!) Now, in my line of work, I've had logic outputs shorted to power, to ground, to each other, for days on end with constant power applied (and some of the chips got damn hot) but I've never burnt one out on that account! In this situation we are talking power differences LESS than 1/1000 of a watt. Logic outputs are designed to take a beating -- temporary shorts etc. They are designed to meet specs at rate levels of voltage under varying power supply conditions and extremes of temperature. If you don't get my gist yet, THERE IS NO PROBLEM with the data lines. -- - John Logajan @ Network Systems; 7600 Boone Ave; Brooklyn Park, MN 55428 - logajan@ns.network.com, john@logajan.mn.org, 612-424-4888, Fax 424-2853