Table 9 – Serial Interface Signals
Signal Description
RX Active high data input
TX Active high data output
GND 0V
RTS Active low flow control input
CTS
Active low flow control output
RTS and CTS are used together to implement hardware flow control when enabled with
AT&K3
DTR
Active low handshaking input
AT&Dn controls how the 9601 SBD Transceiver uses DTR:
•
If set to AT&D0, DTR is always ignored.
•
Otherwise DTR set to OFF places the data port into UART test mode
1
after 10
seconds, or immediately on boot-up. A subsequent transition of DTR to ON returns
the data port to DCE mode and resets it to its power-on state.
DSR
Active low handshaking output
The 9601 SBD Transceiver drives DSR ON when the data port is in DCE mode, and
OFF when the data port is in test mode.
The DTE may use this signal as an indication that the 9601 SBD Transceiver is powered
up and ready to receive AT commands.
RI
Active low ring indicator output
The 9601 SBD Transceiver drives RI ON when it receives a ring alert from the network,
and drives RI OFF after 5 seconds or when the DTE initiates an SBD session, whichever
occurs first.
DCD
Active low handshaking output
DCD is driven ON at all times.
Note that the Ring Indicator (RI) pin is used by the 9601 SBD Transceiver to indicate that a Mobile
Terminated SBD (MT-SBD) message is queued at the Gateway. The Field Application will need to
monitor this pin and use appropriate AT Commands to command the Transceiver to retrieve the MT-SBD
message.
The serial interface may be operated with a 3-wire connection, where only transmit, receive and ground
signals are used. However the 9 wire interface offers better control and is the recommended
implementation. Iridium is only able to provide limited 3-wire interface support. When operating with a 3-
wire connection, the following rules apply:
•
AT&Dn must be set to AT&D0 to ignore the DTR input
•
AT&Kn must be set to AT&K0 to disable RTS/CTS flow control
•
The other output signals may be connected, and operate as follows:
•
CTS driven ON (low)
•
DSR operates as normal
•
RI operates as normal
•
DCD driven ON (low)
1
The UART test mode is provided for factory testing of the data port UART. An FA should never activate
test mode; if it does, the 9601 SBD Transceiver will stop responding to AT commands until the data port
is returned to DCE mode.
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