User`s manual

DIGITAL-LOGIC AG MSLB-P5 Manual V0.3
PRELIMINARY 39
Summary
If the UART should transmit, then set the Bit RTS in the modem control register to ‘0’ and the DTR to
‘1’ befor 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 Condi-
tion
OUTPUTS
/RE = RTSx TE=DTRx 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 = RTSx TE=DTRx A - B R
0
0
1
1
≥ + 0.2V
≤ - 0.2V
1
0
4.3.6 Serial Ports COM3-COM4 RS485
Select the RS422 Interface with:
J108: 1-2 Select COM3 = RS485
J109: 1-2 Select COM4 = RS485
J115: 2-3 Select COM3 = IRQ10 (1-2 = IRQ4 *)
J114: 2-3 Select COM4 = IRQ11 (1-2 = IRQ3 *)
*) if IRQ3/4 used, the driver must handle the shared IRQ3/4 with the COM1/2 !
On the RS422/485-port the signals of UART have the following functions:
Signal of UART Function of RS485
RxDx RO (Receive Line)
RTSx RE/ (Receiver enable) 0 = Enable, 1 = Disable
DTRx DE (Transceiver enable) 1=Enable, 0= Tristate
TxDx DI (Transmission line)
x stands for 3 or 4 depending of the COM3 or COM4 interface.
The RS485 is the same interface as the RS422 with the differenc, that several receiver/transmitter are
in a bus line connected. In this case, the driver must have an access protocol, that make it shure, that
only one transmitter at one time is enabled.