purwin@beta.DEC (06/27/85)
Reply to sychronous dialing
The UDS dialing procedure is not standard by any means, in the recent
Years CCITT addopted V.25 bis procedure which specifies both asynch and
synch protocall. In the synch mode there is two formats one bisync
with 7 bits ASCII plus odd parity and no crc check and second is HDLC protocall.
On top of protocall the operation of interface had been defined to allow
data transfer when modem is off line. The RS232 is lagging behind and therefore
many DTE's have problem to communicate with new DCE's.
The procedure you described is unique to the particular vendor and in light
of new CCITT recomendation should be avoided.The pin 25 is redserved for
test indicator so clearly there is conflict with other devices.
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*I'm faced with a design question on implementing autodial for low speed*
*synch modems (i.e. 4800 bps.)
*
* The only synchronous modem I've got a spec for is a UDS 4800 model.
* Dialout is accomplished by:
* 1) driving pin 12 high;
* 2) driving DTR high;
* 3) waiting a specified time;
* 4) raising pin 25 high for 3.5 seconds;
* 5) providing high and low pulses on pin 25 corresponding to bell
* standard pulse dial signals.
The questions are:
1) does anyone manufacture synchronous modems with some analogy to the
Hayes protocol for async dial out?
answer:
There is modem on the market using v.25bis protocall synchronous
with bisynch format. It is SCHOLAR mnufactured by DIGITAL EQPT. CORP.
The modem has both asynch and synch protocall and either is sofware
selectable.The modem operates at 2400 FD over PSTN
The second method is using secondary data leads for auto dialing
That method is done in DEC's Df126 modem (Bell 201 compatible)
2) Is UDS's method done by anyone else? (i.e. is this a standard?)
answer: As far as I know only UDS did it.
3) If the answer to question 2 is no, then is there a standard?
Answer:
see the introduction ---V.25 bis
I hope that would clarify you questions
Thanks.
-- Jan Purwin
Digital Equipment Corporation