Installation manual

LBI-38987B
11
Except for interconnect calls, all group and individual
calls appear as transmission trunked calls to the radio and
the CEC/IMC. This assures the mobile's quick return to the
Control Channel. Local interconnect is unavailable on
SCAT sites. However, use of the Centralized Telephone
Interconnect System (CTIS or Jessica) is available in the
multisite configuration.
SCAT and Downlink
The SCAT Station GETC provides the control functions
necessary to implement EDACS access to the SCAT service
area. The Downlink is essentially a message conduit
providing a data communication path between the SCAT
station and the CEC/IMC.
The Downlink's modem data is synchronous at 9600
baud using the full duplex operating mode. Data flows
simultaneously in both directions as illustrated in Figure 3.
Data
Blocks
Tx
Rx
Rx
Tx
Data
Blocks
SCAT
CEC/IMC
Uplink
Downlink
Figure 3 - Downlink to CEC/IMC Communication
The SCAT to Downlink format is asynchronous at
19.2K baud using the half duplex operating mode. Data
flows in one direction at a time as shown in Figure 4.
Since these two protocols are different, the Downlink
converts from one format to the other. In addition, both the
SCAT and Downlink perform data error detection and
correction, general control of timer and IO functions (DIP
switch, LED's, UART's, etc.), receive and transmit buffer
management, message scheduling, and Turbo interfacing.
Data
Blocks
OR
BSL
Rx
BSL
Tx
BSL
Rx
BSL
Tx
Data
Blocks
SCAT
Downlink
SCAT
Downlink
Figure 4 - SCAT to Downlink Communication
Wide Area Digital Option
The Wide Area Digital option (SXSF7A) enables the
SCAT station to support Digital Voice communications. A
hardware option (SXMD1D) provides an additional
Rockwell Modem for the SCAT Station GETC. This
enables the SCAT Station GETC to send and receive 9600
baud digital voice to the CEC/IMC using the four wire audio
line.
NOTE
The SCAT software must be 344A3835G2 or
349A9607G5 (or later) to support Digital Voice
communications.
NOTE