Dataplex DPX-213, User Manual

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Section 5
APPLICATIONS
Copyright (C) Dataplex Pty Ltd
5-3
5.4 Synchronous Modes
Mode 2 Synchronous
This is useful for setting up a synchronous auto-answer system or setting up a synchronous
link with an asynchronous terminal and then switching over to a synchronous DTE with an
A/B switch once the call is established.
With AT&M2 set, the DPX-213 allows asynchronous dialling (for example
ATDP1234567). After call establishment (the modem issues the "CONNECT" message),
the modem enters Synchronous Mode and turns on the clocks. It then waits the period
stored in Register S25 before examining the DTR line. This allows time to switch over to a
synchronous DTE. If DTR is high (ON) when S25 expires, the DPX-213 continues in
Synchronous Mode with clocks at the speed of the connection. If DTR is low (OFF), then
the modem takes the action specified by the AT&D setting.
After a call has been placed by the rise of DTR, the remote modem may disconnect and the
local modem may then be in the DTR high but off-line state. If this is the case, it will
answer after S0 rings. If DTR is low and incoming ring is detected, the "RING" message
will be output to the DTE. If DTR is raised while the phone is ringing, the modem will go
on-line in Originate Mode (provided the S0 count has not been reached), or go on-line in
Answer Mode if the S0 value has been passed.
In all other synchronous modes, the AT&D command is ignored and if DTR is on, the
modem is on-line. If DTR is off, the modem will not answer. To allow for auto answer
with DTR down, use the AT&D0 command (Ignore DTR). The modem will then answer
after S0 rings. To allow manual answer on the rise of DTR or answer with DTR high, use
AT&D2 (hang up on fall of DTR). The modem will then answer after S0 rings if DTR is
up, or when DTR rises, provided it is down.
ASYNC/SYNC MODE DTR RISE DTR FALL DTR LOW
ATM2&D0 Ignore DTR. Ignore DTR. Ignore DTR.
AM2&D1 Ignore DTR. On-line Command
State. Do not answer.
AT&M2&D2 Ignore DTR. Hang up and go to
Command State. Do not answer.
AT&M2&D3 Ignore DTR. Execute ATZ and
hang up. Do not answer.
Table 5.3 Mode 2 Synchronous
Mode 3 Synchronous
This mode is the as the AT&M2 mode (as detailed above) except that when the modem
connects it will switch to slave synchronous mode. In this mode, the Tx clock is internally
connected (slaved) to the Rx clock.