Service manual

2000 SERIES RECEIVER DECODER MODULE (RDM)
3-2
March 2000
Part No. 001-3139-502
3.3 RSSI UPDATES
The RDM continues to sample the RSSI every 10
milliseconds and averages the RSSI for each
“WORD”. When this average has been determined,
the RDM sends the updated RSSI information to the
RMM. The upper 4 bits of the byte are unused or 0.
The lower 4 bits of the byte are the RSSI information,
see Table 3-1.
The updated RSSI information is sent via a sec-
ondary RS-232 line (Refer to Figure 3-1). The path is
the RSSI update path where the RDM connects to a
Receiver Multiplexer Module (RMM). This path is a
1200 baud, RS-232 line.
The audio line is a direct connect path between
the RDM and RVM. This line is also an audio 1200
baud line with FSK blank and burst data on initial
decode.
NOTE: See Appendix C and D for frequency chart.
3.4 DISCONNECT
Disconnect by the Mobile can occur one of two
ways. One way is when the RDM is no longer decod-
ing the subaudible “WORD” from the Mobile. The
RDM sends a Receive Time-Out byte by the RS-232
to the RMM. The second way is when the RDM
decodes the Turn-off Code from the Mobile. The
RDM sends a Receive Turn-Off Byte by the RS-232 to
the RMM. See Figure 3-1.
Figure 3-1 2000 RDM BLOCK DIAGRAM
3.5 INTRODUCTION
The Johnson 2000 Repeater Program on 3.5 inch
disk, Part No. 023-9998-297, uses an IBM

personal
computer to program the EEPROM Memory in the
Receiver Decode Module (RDM) Interface Board. To
lessen the chance of programming errors and simplify
operation, the program uses yes/no questions or tog-
gles through the available responses.
The computer is connected directly from the
serial card to the RDM Interface Board. The intercon-
nect cables used are shown in Figure 3-27. The DB-9
to 8-pin modular adapter is connected to the serial port
of the computer and an interconnect cable connects the
adapter to the Interface Board.
NOTE: These connections are for the IBM computer
and may differ from an IBM compatible. In which
case, consult the manuals for your computer for serial
card outputs and connections.
Table 3-1 2000 RDM RSSI INFORMATION
Hex Value DESCRIPTION
7
6
5
4
Strongest RSSI signal level
Weakest RSSI signal level a call will be
started at
3
2*
1
0*
Weakest RSSI level before a call will be
dropped.
Time-Out no update received
No Data received from RDM (generated
by RMM only)
Turn-off Code received from mobile
* Idle state.
RECEIVERS
RDM
RMM
RVM
AUDIO
RS-232