Measurement Computing PCI-COM422/485 - Manual (Page 17)

13
READ/WRITE
31:8 7 6 5 4 3 2 1 0
x x x x X x INT INTPOL INTE
The UART ports are 16C550 compatible. See any 16C550 data sheet for register functions.
AVAILABLE PORTS:
PCI-COM422/485: PORT 1
PCI-COM422/485-2: PORTS 1-2
4.2.2 PORT 1 CLOCK SELECT / INTERRUPT STATUS
BADR2 + 07 hex
READ
7 6 5 4 3 2 1 0
PORT1
TXSEL1
PORT1
TXSEL0
PORT1
CKSEL1
PORT1
CKSEL0
- - INT2 INT1
WRITE
7 6 5 4 3 2 1 0
PORT1
TXSEL1
PORT1
TXSEL0
PORT1
CKSEL1
PORT1
CKSEL0
PORT1
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’.
4.2.3 PORT 2 CLOCK SELECT / INTERRUPT STATUS
BADR3 + 07 hex