Pstn Connection; Led Indicators; Watchdog Functionality - Bausch Datacom DinBox PSTN Reference Manual

The DinBox PSTN(485) modem will detect the DTE port speed (auto baud), number of
data bits and parity type from the "AT" header that precedes every command (in async
mode).
The &W command automatically saves the baud rate, number of data bits, parity and
number of stop bits.
4.3

PSTN connection

The DinBox PSTN(485) modem has to be connected to a PSTN line via the RJ-11
connector.
There are 4 pins connected :
A / B ? connection to the telephone network
A' / B' ? connection for a parallel connected telephone
A is always connected to A' and B is always connected to B'. Therefore it is sometimes
necessary to use a 2-wire telephone cable (only 2 wires in the middle) when the DinBox
PSTN(485) is connected to a digital PABX with analogue telephone lines. A' and/or B'
can be used as signalling lines between the telephone and the PABX.
5.

LED indicators

TxD Transmit Data
RxD Receive Data
DCD Data Carrier Detect
WD Watchdog heartbeat
6.

Watchdog functionality

To prevent a "total lock-up" of the DinBox PSTN(485) a long term watchdog is
implemented. This function is created with a separate RISC micro controller. The micro
controller itself is guarded with it's own internal watchdog (+/- 1 second refresh / WD
LED flash).
The power supply to the communication control processor and the modem module will
be disconnected for a few seconds after +/- 24 hour IF the modem is NOT connected
(inactive DCD signal).
If the reset period is ended and the modem is connected to a remote host (active DCD
signal) the reset will not be conducted.
If the reset period is ended and the watchdog already past a reset, because of an active
DCD signal, the reset will be conducted after +/- 10 minutes !
Otherwise, if the DinBox PSTN(485) is "locked-up" with an active DCD signal the
watchdog will never be able to reset the WAN module.
Bausch Datacom NV
DinBox PSTN Reference manual – V1.3
from DTE to modem
from modem to DTE
from modem to DCE
1 sec on/off
13
A'
A
B
B'