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22 485SDA103798 Manual
B&B Electronics -- 707 Dayton Rd. -- PO Box 1040 -- Ottawa, IL 61350
PH (815) 433-5100 -- FAX (815) 434-7094
Chapter 5 - Software
This chapter covers programming techniques such as
constructing a command string, receiving data and manipulating
data. The various steps and examples are shown in QuickBasic. If
you are programming in another language, these sections can be
used as a guideline for programming the 485SDA10.
Read A/D Command
The Read A/D channels command returns two bytes for each
channel read. The two bytes represent the most significant byte
(MSB) and least significant byte (LSB) of the reading. The MSB is
received first, followed by the LSB. This command requires a data
byte. The data byte is used to specify the number of the highest
channel to be read. All channels less than this channel will be read
as well.
The steps to reading an A/D command are given below:
1. Constructing the command string:
Command$ = “!” + CHR$(addr) + “RA” + CHR$(channel)
The value of channel is equal to the highest channel to be
read.
2. Transmitting the command string:
Print #1, Command$;
3. Receiving the data:
MSB$ = INPUT$(1, #1)
LSB$ = INPUT$(1, #1)
4. Manipulating the data:
reading = (ASC(MSB$) * 256) + ASC(LSB$)
The value of reading is the result of the A/D conversion.
5. Repeat Steps 3 & 4 until each channel has been completed.
Example 5.1 - Read A/D channels 1 and 0 of the module with an
address of 5.
channel = 1
addr = 5
Command$ = “!” + CHR$(addr) + “RA” + CHR$(channel)
Print #1, Command$;