Acrosser AR-B1320 User Manual

Page 56

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5-4

5.4 PROGRAMMING THE RS-485

The majority of the communicative operations of the RS-485 are the same as the RS-232. When
the RS-485 proceeds with the transmission which needs to control the DTR(TXC) signal, the
installation steps are as follows:

Step 1:

Enable DTR (Data Terminal Relay)

Step 2:

Send out data

Step 3:

Wait for data to empty

Step 4:

Disable DTR

NOTE: Please refer to the section of the “Serial Port” in the chapter “System Controller”
for the detailed description of the COM port’ s registers.

(1) Initializing the COM port

Step 1:

Initialize the COM port in the receiver interrupt mode, and /or transmitter interrupt mode. (All
of the communication protocol buses of the RS-485 are the same.)

Step 2:

Disable DTR (Data Terminal Relay) the bit 0 of the address of offset+4 just sets to “ 0”.

åNOTE: Control the AR-B1320 CPU card’ s DTR signal to enable/disable the RS-485’ s TXC

communication.

(2) Send out one character (Transmit)

Step 1:

Enable the DTR signal, and the bit 0 of the address of offset+4 just sets to “ 1”.

Step 2:

Send out the data. (Write this character to the offset+0 of the current COM port address)

Step 3:

Wait for the buffer’ s data to empty. Check the transmitter holding register (THRE, bit 5 of
the address of offset+5), and transmitter shift register (TSRE, bit 6 of the address of
offset+5) so that all sets are set to “ 0”.

Step 4:

Disable the DTR signal, and the bit 0 of the address of offset+4 sets to “ 0”

(3) Send out one block data (Transmit – the data can be more than two characters long)

Step 1:

Enable the DTR signal, and the bit 0 of the address of offset+4 just sets to “ 1”.

Step 2:

Send out the data. (Write all data to the offset+0 of the current COM port address)

Step 3:

Step 4:

Disabled DTR signal, and the bit 0 of the address of offset+4 sets to “ 0”