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LTC2870/LTC2871
32
28701fb
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Figure43. LTC2871: Using External Connections for RS485 (Half or Full Duplex) and RS232 (Full Duplex)
Figure44. Schematic Implementation of Figure43, Above, Using a Single Pair of Wires for the Bus I/O
Typical applicaTions
28701 F50
LTC2871
1.7V TO V
CC
3V TO 5.5V
DX485
RX232
RX485
DX232
TE485
H/F
DIN1
DIN2
Y
DOUT1
DOUT2
Z
A
B
RIN2
RIN1
DI
ROUT1
RO
ROUT2
V
L
V
L
V
CC
GND
RS485
RS485
FULL-DUPLEX
DX232 = 0
RX232 = 1
TE485 = X
H/F = 0
RS485
HALF-DUPLEX
DX232 = 0
RX232 = 1
TE485 = X
H/F = 1
RS485
RS485
CONTROLLER
RS485
RS485
RS232
FULL-DUPLEX
DX232 = 0
RX485 = 1
DX232 = 1
RX232 = 0
TE485 = 0
H/F = X
RS232
RS232
RS232
RS232
RS485
DI
RO
TxAY
RxBZ
V
CC
V
L
H/
F
CH
DX485
TE485
RX232
DIN1
DI
RX485
DIN2
DX232
ROUT1
RO
FEN
ROUT2
SW
CAP
V
DD
V
EE
GND
LB
DOUT1
Y
Z
RIN1
A
B
DOUT2
RIN2
L1
10µH
C1
220nF
C4
2.2µF
C2
1µF
C3
1µF
LTC2871
RS485 DRIVER
ENABLE
RS485
RS232
28701 F51
Logic input pins not shown are tied to a valid logic state. External Components not shown.
This configuration allows for a two-wire interface (top two wires) operating in either RS485
half-duplex or RS232 full-duplex mode. A second pair of wires (bottom two wires) allows a
second RS232 interface operating in full duplex mode and also allows for RS485 operating in
full duplex mode. The two-wire application is comparable to the LTC1387 data sheet, Figure 14.
Two logic gates were added (optional) to simplify
the control signals needed from the controller.
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