DIGITAL-LOGIC AG
MSMX104 Manual V1.3
15
4
D
ETAILED
S
YSTEM
D
ESCRIPTION
4.1 Programming the RS422/485 port
On the RS422/485-port the signals of UART have the following functions:
Signal of UART
Function of RS485
RxD
RO (Receive Line)
RTS
DE (Transceiver enable) 1=Enable, 0= Tristate
TxD
DI (Transmission line)
The /RE is harware straped to low, and the receiver is always enabled.
Typical Application
Summary
If the UART should transmit, then set the Bit RTS in the modem control register to ‘0’ before the databyte
is sent to the transmit register.
If the UART should receive, wait on the receive buffer full flag as usual. Nothing special must be done,
since the RS422/485 receiver is always enabled.
FUNCTION TABLES
ADM489 Transmitting
INPUTS
Line
Condition
OUTPUTS
/RE = GND
TE=RTS
DI
B
A
0
0
0
0
1
1
0
1
1
0
X
X
no fault
no fault
X
fault
0
1
Z
Z
1
0
Z
Z
ADM489 Receiving
INPUTS
OUTPUTS
/RE = GND
TE=RTS
A - B
R
0
0
1
1
≥
+ 0.2V
≤
- 0.2V
1
0
