F81438
5 Function Description
5.1
Mode Selection
The F81438 drivers and receivers can be configured to operate either as the standard RS-232 or
RS-485 / RS-422 devices. It can be reconfigured into four operating modes, and be selected by 2
configuration pins. The table below shows how to use the configuration pins to select the function
you want.
TABLE 1: Mode Select Configuration
Pin 2 Mode_1 Pin 23 Mode_2
Mode
Status
0
1
1
0
1
0
1
0
Pure RS-232
3T/ 5R RS-232.
RS-485 Receiver Half Duplex 1T/1R RS-485
RS-485 Driver Half Duplex
Pure RS-422 Full Duplex
1T/1R RS-485
1T/1R RS422 mode
The RS-485 / RS-422 drivers have the differential outputs and receivers have the differential
inputs. RS-232 drivers and receivers are single-ended with the inverting outputs. The following table
shows the characteristic of F81438 in RS-485 / RS-422 Full & Half Duplex mode.
TABLE 2: RS-232: MODE 01
DRIVERS
RECEIVERS
Input
0
Output
ꢀ5V
Input
ꢀ 3V
ꢀ-3V
Open
Output
0
1
1
1
ꢀ-5V
ꢀ-5V
Open
TABLE 3: RS-485 Driver & Receiver Half DUPLEX: MODE 10, MODE 11
T
RANSMITTING
RECEIVING
Inputs
Outputs
Inputs
Outputs
DE/RE
TXIN
TX(A)
TX(B)
DE/RE
RX(A) - RX(B)
RXOUT
1
1
1
0
0
1
1
0
1
1
0
0
0
x
High-Z
x
High-Z
> -50mV
ꢀ <-200mV
Open / Shorted
1
0
1
0
x
High-Z
High-Z
Jan, 2012
V0.11P
7
FINTEK [ FEATURE INTEGRATION TECHNOLOGY INC. ]
