AL5068S Designer’s Guide
No. AL5068S-E00-105
Altec Electronic AG
Seite 13 / 25
Table 3.4 / Serial Interface Signal Descriptions
~RTSTTL IA
Request To Send (TTL Active Low).
~RTS is used to condition the local
modem for data transmission and, during half-duplex operation, to control
the direction of data transmission.
On a full-duplex channel, RTS-OFF maintains the modem in a non-
transmit mode. A non-transmit mode does not imply that the ISDN link
have been terminated.
RTS input ON causes the modem to transmit data on TXD when ~CTS
becomes active.
~RXDTTL OA
Received Data (TTL Active Low).
The modem uses the ~RXD line to
send data received from the ISDN line to the DTE and to send modem
responses to the DTE. During command mode, ~RXD data represents the
modem responses to the DTE. Modem responses take priority over
incoming data when the two signals are in competition for ~RXD.
~TXDTTL IA
Transmitted Data (Active Low).
The DTE uses the ~TXD line to send
data to the modem for transmission over the ISDN network or to transmit
commands to the modem. The DTE should hold this circuit in the mark
state when no data is being transmitted or during intervals between
characters.
~CTSTTL OA
Clear To Send (TTL Active Low).
~CTS is controlled by the modem to
indicate whether or not the modem is ready to transmit data. ~CTS ON,
together with the ~RTS ON, ~DSR ON, and ~DTR ON (where
implemented), indicates to the DTE that signals presented on TXD will be
transmitted to the ISDN network. ~CTS OFF indicates to the DTE that it
should not transfer data across the interface on TXD. ~CTS ON is a
response to ~DTR ON and ~RTS, delayed as may be appropriate for the
modem to establish an ISDN connection.
~RITTL OA
Ring Indicate (TTL Active Low).
~RI output ON (low) indicates the
presence of ALERTING on the ISDN network.
~DSRTTL OA
Data Set Ready (TTL Active Low).
~DSR indicates modem status to the
DTE. ~DSR OFF (high) indicates that the DTE is to disregard all signals
appearing on the interchange circuits except Ring Indicator (~RI).
~DCDTTL OA
Data Carrier Detect (TTL Active Low).
~DCD output is ON (low) when a
link is established over the ISDN network and is OFF (high) when no link
is present.
~DTRTTL IA
Data Terminal Ready (TTL Active Low).
The ~DTR input is turned ON
(low) by the DTE when the DTE is ready to transmit or receive data. ~DTR
ON prepares the modem to be connected to the ISDN network, and
maintains the connection established by the DTE (manual answering) or
internally (automatic answering). ~DTR OFF places the modem in the
disconnect state under control of the AT Command AT&Dx
