Measurement Computing PCI-COM422/485 User Manual
Page 18
14
READ
7
6
5
4
3
2
1
0
PORT2
TXSEL1
PORT2
TXSEL0
PORT2
CKSEL1
PORT2
CKSEL0
-
-
INT2
INT1
WRITE
7
6
5
4
3
2
1
0
PORT2
TXSEL1
PORT2
TXSEL0
PORT2
CKSEL1
PORT2
CKSEL0
PORT2
ECHOEN
-
-
-
INTx
Interrupt status for each port. The same signals are connected to this read register for all ports.
CKSEL1:0
UART clock select. This allows for data rates to 460.8 Kbps and different data rates on
each port. These settings are per-port:
CKSEL1
CKSEL0
UART CLOCK
Max Data Rate
0
0
1.8432 MHz
115.2 kbps
0
1
3.6864 MHz
230.4 kbps
1
0
7.3728 MHz
460.8 kbps
TXSEL1:0 Transmit data control select. This allows for controlling the Transmit Data driver. The default
mode for RS485 is ‘Auto Enable’. This mode is recommended for all RS485 communication.
TXSEL1
TXSEL0
Transmit Control
Duplex Mode
0
0
Auto Enable
Half
0
1
RTS
Enable Half
1
0
DTR
Enable Half
1
1
Transmit ‘ON’
Full – RS422 Mode
ECHOEN 1:0 Echo enable/disable. When set low, this enables the hardware to echo the transmitted data to the
receiver. When set high, this disables the ‘Receiver Enable’ control signal on the RS485 transceiver while data is
being transmitted. Therefore, the transmitted data are not echoed to the receiver.
For TXSEL0:1 = ‘11’, ECHOEN has no function since this is full duplex mode and the transmitter and receiver are
always ‘ON’.