Datasheet
LTC2870/LTC2871
19
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For more information www.linear.com/LTC2870
FuncTion Tables
Table 5. LTC2871 CH2 CONTROL
CH2 DX232 RX232
RS232 RECEIVER INPUTS RS232 DRIVER OUTPUTS
COMMENTSRIN1 RIN2 DOUT1 DOUT2
X 0 1 Hi-Z Hi-Z Hi-Z Hi-Z Both Drivers and Receivers Disabled
0 0 0 5kΩ 5kΩ Hi-Z Hi-Z Both Receivers Enabled, Both Drivers Disabled
0 1 1 Hi-Z Hi-Z Driven Driven Both Receivers Disabled, Both Drivers Enabled
0 1 0 5kΩ 5kΩ Driven Driven Both Receivers and Drivers Enabled
1 0 0 5kΩ Hi-Z Hi-Z Hi-Z Channel 2 Drivers and Receivers Disabled
1 1 1 Hi-Z Hi-Z Driven Hi-Z Channel 2 Drivers and Receivers Disabled
1 1 0 5kΩ Hi-Z Driven Hi-Z Channel 2 Drivers and Receivers Disabled
Table 6. RS485 Driver Mode (TE485 = 0)
DX485 OR DXEN DI CONDITIONS Y Z
0 X No Fault 125kΩ 125kΩ
1 0 No Fault 0 1
1 1 No Fault 1 0
X X Thermal Fault 125kΩ 125kΩ
Table 7. RS485 Receiver Mode (LB = 0)
RXEN OR RX485 A - B (NOTE 5) CONDITIONS RA, RO
1 X No Fault Hi-Z
0 < –200mV No Fault 0
0 > 200mV No Fault 1
0 Inputs Open or Shorted Together (DC) Failsafe 1
X X Thermal Fault Hi-Z
Table 8. RS485 Termination (485/232 = 1 for LTC2870)
TE485 H/F, LB CONDITIONS R (A TO B) R (Y TO Z)
0 X No Fault Hi-Z Hi-Z
1 X No Fault 120Ω 120Ω
X X Thermal Fault Hi-Z Hi-Z
Table 9. RS485 Duplex Control (485/232 = 1 for LTC2870)
H/F RS485 DRIVER OUTPUTS RS485 RECEIVER INPUTS
0 Y, Z A, B
1 Y, Z Y, Z
Table 10. LTC2870 Loopback Functions
LB RXEN MODE
0 X Not Loopback
X 1 Not Loopback
1 0 Loopback (RA = DY, RB = DZ)
Table 11. LTC2871 Loopback Functions
LB RX232 RX485 MODE
0 X X Not Loopback
X 1 1 Not Loopback
1 0 1 Loopback RS232 (ROUT1 = DIN1, ROUT2 = DIN2)
1 1 0 Loopback RS485 (R0 = DI)
1 0 0 Loopback All (ROUT1 = DIN1, ROUT2 = DIN2, RO = DI)
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