info-vax@ucbvax.ARPA (07/09/85)
From: Sang K. Cha <CHASK@SU-SIERRA.ARPA> Could anybody please tell me how many pins are needed in minimum for VT241 color graphics terminal to be locally connected to VAX ? I also have DECTALK unit to go in serial with VT241. Any experience of these, relevant to site preparation, would be appreciated. Sang CHASK@SIERRA.ARPA -------
info-vax@ucbvax.ARPA (07/09/85)
From: Peter Stokes <stokes%cmc.cdn%ubc.csnet@csnet-relay.arpa>
For VT220, VT240 the minimum pins required are 2,3 and 7. These are
Tx, Rx and common. This is assuming you have the VTXX0 configured
to operate in X-on X-off flow control. The terminal configuration on
the Vax should be that of no modem. I imagine the wiring for a
VT24*1* is the same but I'm not sure.....
peterinfo-vax@ucbvax.ARPA (07/09/85)
From: Richard Garland <OC.GARLAND@CU20B.ARPA> 3 pins are fine. 1,2, & 3. We use 4 conductor phone line and phone janck built into the RS232 connectors (made by MOD-TAP). This uses one other line (I think 20) but its not needed to make things work. By the way, the MOD-TAP system is a great convenience. Rg (I don't work for them) -------
info-vax@ucbvax.ARPA (07/09/85)
From: Richard Garland <OC.GARLAND@CU20B.ARPA> By the way as some have suggested connecting pins 1,2, & 3, others suggest 7,2, &3 you might note that 1 is defined as protective ground and 7 as signal ground or common. On most DEC terminals and asynch interfaces (i.e. VT series, DZ11, DMF32) pins 1 and 7 are hard wired together. So not to worry, either 1 or 7 works fine. (not true on some non-DEC terminals) Rg -------
info-vax@ucbvax.ARPA (07/11/85)
From: Bob Sutterfield <sutter%ohio-state.csnet@csnet-relay.ARPA> As Richard Garland @CU20B has pointed out, pins 1 (protective gnd) and 7 (signal gnd) are wired together on most DEC VT devices. I had this confirmed for me in a most distressing situation by a local Terminals Field Service rep: My standard station cabling connects pins 2, 3, 7, and 20, with 2 and 3 crossed (standard `null modem'). When we wired an office complex with many users on Rainbows (acting like VT102's) to Xyplex cluster controllers, most came out allright. When one secretary turned hers on one morning, with new station cable connected to COMM port, she noticed funny lights, sounds, and smells coming from her machine. Upon further investigation (most of the day), it turned out that the office had been wired for power about 23 years ago, before it was common practice to wire the ground plug of the 120V outlet to a real ground. All the `ground plugs' in that complex are tied to the neutral leg of the AC!!!! This makes them float wherever they happen to go, with no reason to agree on a common reference. In short: ground plug goes to chassis of Rainbow, into RS232 asynch controller area, where pin 1 (`protective' ground, remember?) is wired to pin 7 (signal ground), thence over station cable into cluster controller (on pin 7), where pins 1 and 7 aren't wired together, and pin 1 is really wired to power ground. Well, it turns out that there happened to be somewhere near *82 volts* between the two `grounds' that day. That voltage pushed current through the ICs on boards in both the cluster controllers and the Rainbow. Chips really exploded, and signal traces on the printed circuit boards acted like fuses (several layers deep). And, I had no idea what the problem with the cluster was (thought it was software at first), so I used some (clear throat) ineffecient diagnosis techniques, roasting yet more equipment. The carnage: Two Rainbow motherboards Two Xyplex cluster controllers Probably around $7000 in all. All was replaced under maintenance, although neither Xyplex nor DEC really should have - it was a personal-favor-for-a-big-customer situation on both counts. The moral: Check the validity of your grounds before installing any DEC terminal products in an area with older wiring. Mothers, don't let your babies do what I done...
info-vax@ucbvax.ARPA (07/12/85)
From: dual!mordor!seismo!ut-sally!shell!buck@BERKELEY (Lester Buck)
By the way, what is the MOD-TAP you mention? Is it one of those
smart RS-232 boxes that flips 2 & 3 as necessary?
Thanks,
A. Lester Buck @ Shell Development Co.
{ihnp4, pur-ee, ut-sally}!shell!buckinfo-vax@ucbvax.ARPA (07/12/85)
From: Richard Garland <OC.GARLAND%CU20B@COLUMBIA.ARPA>
> what is the MOD-TAP you mention?
MOD-TAP is a line of products which enable you to use telephone type
punch-blocks, multi-pair cable, modular jacks (RJ11) and other similar
type phone equipment for connecting RS232 terminals.
The particuler product which I mentioned is an RS232 connector (25 pin)
which instead of having a cable comming out the back, has a phone jack
(those cute little connectors used to plug your phone into the wall).
They make 4 conductor and 6 conductor varieties (maybe 8 conductor also)
plus system-DTE, terminal-DTE, system-DCE, terminal-DCE varieties.
Anull modem cable consists of 1 System-DTE connector, 1 Terminal-DTE
connector, and 1 phone cable with phone jacks.
Their address is
MOD-TAP system
P.O. Box 706
Harvard MA, 01451
The stuff is used at DECUS by DEC to connect all their stuff together.
Rg
(usual disclaimer)
-------