Comtech EF Data MIDAS 4 System and Design - Manual (Page 123)

System and Design Manual, Revision 2
Traffic Node 6–25
E E F F B B U U S S 1 1
EFBUS1 is the SNM-1000 to Comtech EF Data Modem/Radio Frequency
Terminal (RFT) EIA-485 bus interface. This interface allows the SNM-1000
to communicate with and control Comtech EF Data’s data and video modems.
The EFBUS1 uses a master-slave architecture, with SNM-1000 being the
master. All other devices are slaves, and cannot transmit on the bus until the
master requests a response.
The physical transmission protocol of the bus is asynchronous, 19.2 kbps, 8
data bits, no parity and one stop bit. EFBUS1 shares the 9-pin connector with
EFBUS2. The pinout is described in Table 6-2
Table 6-2. EFBUS1 Port Pinout
Connector Type 9-pin D subminiature, female
Signal type EIA-485
Pin # Name Pin # Name
1 MSGND 5 MS_RD/SD-
2 BP_DF 6 MC_RD/SD+
3 BP_MF 7 MC-RD/SD-
4 MS_RD/SD+ 8 MCGND
Each end of the bus is terminated with 120
Ω
resistors. The EIA-485 bus can support
up to 30 physical devices with a maximum of 50 feet (15.24 ms.) of twisted pair cable
when properly terminated.
E E F F B B U U S S 2 2
EFBUS2 is reserved for future releases and is not currently utilized.