serial communication format

Hi
Im new to serial communication. I try to understand how to reed and write to a serial device from a PLC. I use Beckhoff PLC with RS232 port and serial com library.

In the datasheet of the device they say that output is ASCII and in this format: (This is a distance)

[DD]D.DD<CR><LF>
In this configuration, each sample consists of a string of characters as follows: 4
to 6 distance followed by <CR><LF>. characters (possible values from 0.00 to
999.99 inches in 1/100ths of an inch in English output, or 0 to 99999 mm metric)​

Values enclosed in [] will not appear if they consist only of leading zeros.

1. So how can this be understand? and how can it be read by a read block? What kind of read block would I use: I have receive byte and receive string available...
2. I belive i must use string right? How will that string look like after receiving a number? will it include <CR><LF>,? what ecsactly are thouse?
3. There are several other readings like this one:

ASCII Data format, Low Level Sensor Outputs Only​

[​

RRRRRR]R<TAB>[SSS]S<TAB>[AAA]A<TAB>[TTT]T<CR><LF>
In this configuration, each sample consists of characters as follows: 1 to 7 range
characters (possible values from 0 to 4.19 million, decimal format), SPACE, 1 to
4 signal strength characters (0 to 1023), SPACE, 1 to 4 ******t light level
characters (0 to 1023), SPACE, 1 to 4 sensor temperature characters (0 to 1500 in​

0.1oF per unit), <CR><LF>.

How can I decide witch one is what? like saving in two different strings...

Now I like to send a ASCII code to the sensor: one of its settings are:

Set Sample Interval​

3-8 bytes ASCII Code: S<Interval>
(20 <= Interval <= 9999999)​

Input switch code: 8<Rate Code>

How to do this? just send a string like "S9999999" or S<9999999>
What do they mean by input switch code?


Sorry for this basic questions, but I like to understand this


Thanks!

Best regards
Han sPettersson

Hi Han,

I am doing the same task. I am trying to read out the temperature through RS 232 communication in Beckhoff PLC.

First of all ,you have to use fast track programme which can exachange
the Input and Output through your terminal(which should define in Twin CAT system manager as priority task).

Second, You need to send string and receive string (Just to understand the formate).

That might be can help.

Be aware, which module you are using and which data types with defalut function blcok you are using to communicate .That's really important.

But i have now problem that I am not able to read out the data correctly.


Hope it can help you.

<CR>, <LF> and <tab> are control characters




The greater than/less than brackets that enclose the data are for documentation purposes, but are not part serial data string.