AR-B1474 User¡¦s Guide

9-2

Example 1: Select the 10th bank of the MEM1 on the AR-B1474. The AR-B1474 is using 27C020 (256K*8), and
the base port is &H210.
100 base_port=&H210
110 OUT base_port+0,&H59
Example 2: Select the 40th bank of MEM3 on the AR-B1474. The AR-B1474 is using 27C040 (512K*8), and the
base port is &H390.
200 base_port=&H390
210 OUT base_port+0,&HD7
9.2 PROGRAMMING RS-485
The majority communicative operation of the RS-485 is in the same of the RS-232. When the RS-485 proceeds
the transmission which needs control the TXC signal, and the installing steps are as follows:
Step 1: Enable TXC
Step 2: Send out data
Step 3: Waiting for data empty
Step 4: Disable TXC
NOTE: Please refer to the section of the “Serial Port” in the chapter “System Control” for the detail description of
the COM port’s register.

(1) Initialize COM port

Step 1: Initialize COM port in the receiver interrupt mode, and /or transmitter interrupt mode. (All of the
communication protocol buses of the RS-485 are in the same.)
Step 2: Disable TXC (transmitter control), the bit 0 of the address of offset+4 just sets “0”.
NOTE: Control the AR-B1474 CPU card’s DTR signal to the RS-485’s TXC communication.

(2) Send out one character (Transmit)

Step 1: Enable TXC signal, and the bit 0 of the address of offset+4 just sets “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 empty. Check 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) are all sets must be
“0”.
Step 4: Disabled TXC signal, and the bit 0 of the address of offset+4 sets “0”