F81438 Datasheet, PDF (7/20 Pages) Feature Integration Technology Inc. – Single 5V RS232/RS422/RS485 Multiprotocol

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.
Pin 2 Mode_1
0
1
1
0
TABLE 1: Mode Select Configuration
Pin 23 Mode_2
Mode
1
Pure RS-232
0
RS-485 Receiver Half Duplex
1
RS-485 Driver Half Duplex
0
Pure RS-422 Full Duplex
Status
3T/ 5R RS-232.
1T/1R RS-485
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.
Input
0
1
Open
DRIVERS
TABLE 2: RS-232: MODE 01
Output
　5V
　 -5V
　 -5V
Input
　 3V
　-3V
Open
RECEIVERS
Output
0
1
1
TABLE 3: RS-485 Driver & Receiver Half DUPLEX: MODE 10, MODE 11
TRANSMITTING
RECEIVING
Inputs
Outputs
Inputs
DE/RE
TXIN
TX(A)
TX(B)
DE/RE
RX(A) - RX(B)
1
1
0
1
1
x
1
0
1
0
1
x
0
> -50mV
0
x
High-Z
High-Z
0
　 <-200mV
0
Open / Shorted
Outputs
RXOUT
High-Z
High-Z
1
0
1
7
Jan, 2012
V0.11P