C H A P T E R 3 - S E R I A L I N T E R F A C E
8
1 - 8 7 7 - 8 7 7 - 2 2 6 9
w w w . b l a c k b o x . c o m
R S 4 8 5 - M D R 2 9 4 A
The RS-485 interface uses a Differential Data Transmission that can help nullify the effects of ground shifts
and induced noise signals that can appear as common mode voltages on a network.
The MDR294A implements a RS-485 (2-wire Half Duplex) multi-drop interface. Typically, a RS-485 bus will
consist of a master and several slaves. The nodes will have unique addresses and can send addressed
packets to specific nodes. Because the bus is half duplex, no two nodes should try to talk at the same time.
The MDR294A does not have a RS-485 address, therefore, it will transmit all RS-485 traffic over the RF.
Conversely, as soon as a MDR294A receives a packet over the RF, it will transmit the packet over the RS-
485 bus.
Note: When using RS485 (2-wire Half Duplex), a RS485 to RS232 converter is required to configure the
unit.
F i g u r e 9 : R S 2 3 2 - 4 8 5 C o n v e r t e r
T A B L E 4 : M D R 2 9 X T E R M I N A L B L O C K P I N O U T
T E R M I N A L
B L O C K P I N
S I G N A L N A M E
D E S C R I P T I O N
1
VCC
6-18V (1.3A required)
2
485 -
485B
3
N/C
No Connect
4
N/C
No Connect
5
485 +
485A
6
GND
Ground
1
6
+5V
GND
B-
A+
RS
232
RS48
5
1
6
Power Connector
Terminal Block
RS232-485 Converter
MDR294A
485 -
485 +
Many simple 2 or 4-wire converters do not provide hardware flow control capabilities and
therefore require Handshaking to be disabled in the Black Box Configuration Utility to
configure the radio. Check with your converter Manufacturer for any specific requirements.
DESIGN TIP
