B&B Electronics RS-485 manual Read Digital I/O Command, Command$ = ! + CHR$addr + RD

‘Get the value of channel 1

MSB$ = INPUT$ (1, #1)

LSB$ = INPUT$ (1, #1)

reading1 = (ASC(MSB$) * 256) + ASC(LSB$) ‘Get the value of channel 0

MSB$ = INPUT$ (1, #1)

LSB$ = INPUT$ (1, #1)

reading0 = (ASC(MSB$) * 256) + ASC(LSB$) The value of reading1 is the result of the A/D conversion on channel 1. The value of reading0 is the result of the A/D conversion on channel 0.

Read Digital I/O Command

The Read Digital I/O command returns a byte which represents the states of the 3 digital input and 3 digital output states. Bits 3-5 correspond to the states of digital inputs 0-2, and bits 0-2 correspond to the states of digital outputs 0-2. If a bit is a 0 then the digital state of that digital I/O is LOW. If a bit is a 1 then the digital state of the I/O is HIGH.

The steps to reading a digital I/O command are given below:

1.Constructing the command string:

Command$ = “!” + CHR$(addr) + “RD”

2.Transmitting the command string:

Print #1, Command$;

3.Receiving the data:

Reply$ = INPUT$ (1, #1)

4.Manipulating the data: states = ASC(Reply$)

5.Determining an I/O’s status status = states AND mask

6.Repeat Step 5 until the status of each I/O has been determined.

By “ANDing” the value of states with the appropriate mask of an I/O line, the status of can be determined. If status is equal to zero then the I/O line is LOW. If status is not equal to zero then the I/O line is HIGH. Table 5.1 shows the mask values for each I/O.

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