| Title: | The Digital way of working |
| Moderator: | QUARK::LIONEL ON |
| Created: | Fri Feb 14 1986 |
| Last Modified: | Fri Jun 06 1997 |
| Last Successful Update: | Fri Jun 06 1997 |
| Number of topics: | 5321 |
| Total number of notes: | 139771 |
I monitor an e-mail account for readers-comments (errors, ommisions and the like) on Digital's networking product documentation. We received the following inquiry from a DECserver 700 customer in New Zealand who is looking for documentation on LAT and TELNET drivers. Because doc groups are not set up to do customer support--although we surely do try to help customers whenever we can, I have advised him to contact his local Digital rep. I am also posting his inquiry here because this notesfile has proved to be a good means of getting a customer in touch with the Digital rep he needs. Regards, Alice ------------------------------------------------------------------------------- Appended inquiry about DECserver 700 >From: LKGMTS::LKGMTS::MRGATE::"DASMTS::UMC::[email protected]" >To: TNPUBS::PHALEN >CC: >Subj: DECServer700 > >From: NAME: JEFF VARTIANEN ><[email protected]@umc@DASMTS@ECOM> >To: NAME: Digital <[email protected]@umc@DASMTS@ECOM> > >We recently purchased 11 off Decserver700 Terminal servers as part of >an MIS Project. However we are are having problems communicating with Modbus >devices connected to the serial ports of the servers. Can you supply detailed >technical documentation explaining operation of LAT and TELNET drivers for >Decserver700. Standard doc does not explain algorith for flushing comm >buffers, etc. > >Thanks >Jeff Vartiainen >Systems Engineer >CHH Pulp & Paper Ltd >Kinleith >New Zealand
| T.R | Title | User | Personal Name | Date | Lines |
|---|---|---|---|---|---|
| 4361.1 | Oooer, what a way to end the week | BBPBV1::WALLACE | UNIX is digital. Use Digital UNIX. | Fri Jan 12 1996 12:47 | 39 |
Oh boy.
In my N years at Digital I have succesfully made terminal servers talk
to most things, and there are very few words which cause concern
when people talk about terminal servers. But one which does is Modbus,
a dinosaur-age protocol still widely used for talking to industrial
controllers from the Modicon company (for whom I used to work).
Modbus comes in two flavours; ASCII mode and RTU mode.
ASCII mode uses only printable characters and is a nice reliable way of
making things work. It has message delimiters and other nice stuff.
The bad news, with terminal servers, is RTU mode. To get max thruput it
uses all the characters 0 - 0xff. Worse, the protocol has no byte
count, no terminators. End of message is indicated by an
inter-character gap of some small number of characters equivalent,
typically a small number of milliseconds. The gap makes a timer fire in
the Modicon, which then goes to read the message.
The consequence of this is that ANY comms device which packetises the
data from the host (be it a terminal server from Digital or an
error-correcting modem from Hayes) is an unsuitable device for Modbus
RTU mode, because the few millisecond inter-character gap between
packets will be interpreted by the Modicon device as end of message,
and the message will be rejected because it's incomplete. Then the next
packet comes along, and is rejected because it's not a valid Modbus
message.
You can't even fix it by lowering "circuit timers" and the like.
Impact: if you insist on RTU mode, you need hardwired serial lines, not
terminal servers.
I'll send the author of .0 some sample VMS code that has been seen to
work.
regards
john
| |||||
| 4361.2 | Other avenues ? | BBPBV1::WALLACE | UNIX is digital. Use Digital UNIX. | Fri Jan 12 1996 12:53 | 8 |
Anybody in Digital Australia's manufacturing folks reading this ? e.g.
is Pete Huish still around ?
They'd probably be good people to talk to to progress this to a
satisfactory conclusion.
regards
john
| |||||
| 4361.3 | Thanks | TNPUBS::PHALEN | Fri Jan 12 1996 13:10 | 8 | |
John, Thanks for your responses. I have located Peter Huish in NLO (Newcastle, Australia) and I will forward the inquiry to him. Regards, Alice | |||||
| 4361.4 | Pointer | IROCZ::MORRISON | Bob M. LKG1-3/A11 226-7570 | Fri Jan 12 1996 16:32 | 2 |
In general, questions about DECservers should be posted in IROCZ::TERMINAL_SERVERS. | |||||
| 4361.5 | thanks for pointer | TNPUBS::PHALEN | Tue Jan 16 1996 15:47 | 6 | |
Thanks, Bob, I will post the inquiry there as well. regards, alice | |||||