ASCII Command String

Hi, all

I have a little problem here. I've got an assignment where i'm supposed to write a program in the TIA Portal that sends ASCII-commands to a temperature monitoring system for grain silos. Works on the RS-485 protocol, 9600 baud, 1 stop bit and 8 databits and it responds to ASCII-commands like:

$01T11<CR> - Gets temperatures from all the sensors in the network

"$[Adress][Temperature command][Sensor line][Checksum][Carriage return]"

and...

$01P1<CR> - Ping controller

I've been able to ping the controller from a hyper terminal using an RS-485-USB-converter. I Just entered "$01P1" and hit the enter-key twice - once to send the messege and once to send "Carriage Return".

in my program i entered the whole messege i wanted to send into a String - $01P1<CR> but the netcontroller doesn't seem to respond or understand. 

Also when the ASCII-Module sends something both TX and the RX-led's blink. And this started recently.

I'm a complete novice when it comes to ASCII-communication so i'm hoping someone can shine some light on the subject

thanks :)

Hello,

missing important info what exact controller with HW comm module, what exact SW for programming? You can post zipped pictures from DB where you prepare message, BYTE per BYTE, I want to see it. Also piece of code ehere you have comunication instructions can be fine. Also pls give description with ASCII chars what really you want send for comparing with your DB where you have bytes for send defined.

1SI Modbus/Uss controller 6es7-138-4df010ab0

ET 200s CPU

I'm sending the messege from and array of bytes with $01P1<CR> written hexadecimally and i'm using the S_Send and S_RCV-function blocks

Hello,

ok for sure now, pls give exact byte sequence in hex (check that from documentation) not in ASCII chars, because it can be problem like $01, this can be also hex 01 in char representation. Pls give that hex byte sequence exactly from documentation, or also if that working from Hyperterminal then show each char as hex representation. This can be better. Also good hint can be in any case give info about needed value of send bytes with that example, in this case we can also imagine better how much bytes need to be send.

Update: or attach that pdf documentation or link to that documentation.

Byte sequence:

24 30 31 50 31 3c 40 52 3e

ASCII-sequence:

$01P1<CR>

Hello,

very sry, probably I see still missunderstanding. Look to your first post where is Checksum byte. I think better will be attach that documentation or link to it.

smiffy

Just a guess, but maybe the <CR> are not actually meant to interpreted literally? Could it be that Hypreterminal uses trhe <XX> to mark a special control character (in this case carraige return or ASCII code 13)? So <CR> is not sent as 3c 40 52 3e but actually sent as 13.
You coild verify this by actually monitoring what is send by using a telegram trace.

But a quick test could be to try the sequence (replacing <CR> (3c 40 52 3e) with ASCII 13).

24 30 31 50 31 13

I was thinking something along similar lines. Thanks alot. I'll try that tommorrow. Could you elaborate on "Telegram trace"?

Now i have to battle these signal reflections. The wire is about 50 cm long so i'll need a ~500 Ohm resistor by my calculations