AL7020S Designer’s Guide
Doc. No. DG_7020B
Altec Electronic AG
Seite 11 / 32
Table 3-3. Signal Descriptions (Cont'd)
Label
I/O Type
Signal Name/Description
The Serial interface signals are TTL-level signals.
~RTSTTL IB
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 all GSM signals have been
removed from the link. RTS OFF may be ignored if the modem is optioned to
strap ~CTS ON; this allows the modem to receive from the DTE even though
RTS is OFF.
RTS input ON causes the modem to transmit data on TXD when ~CTS
becomes active.
~RXDTTL OB
Received Data (TTL Active Low).
The modem uses the ~RXD line to send
data received from the telephone line to the DTE and to send 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 (TTL Active Low).
The DTE uses the ~TXD line to send
data to the modem for transmission over the telephone line 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 OB
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.
~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 a connection.
~RITTL OB
Ring Indicate (TTL Active Low).
~RI output ON (low) indicates the
presence of an incoming call.
~DSRTTL OB
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 OB
Data Carrier Detect (TTL Active Low).
When AT&C0 command is not in
effect, ~DCD output is ON when a link is established or OFF when no link is
established.
~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 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 &Dn command. The effect of ~DTR ON and ~DTR OFF
depends on the &Dn command.
