Need help capturing a response.

electromanj

Hello everyone! I have a question that is probably simple for you, but I don't know where to start.

I am sending commands to a controller and then getting a response. This is my code:

pub send_telegram
  waitcnt(clkfreq/100+cnt)
  debug.str(string("sending telegram",cr)) 
  waitcnt(clkfreq*2+cnt) 'wait for at least 3.5 character intervals
  plc.tx($01)
  plc.tx($03)
  plc.tx($40)
  plc.tx($9B)
  plc.tx($00)
  plc.tx($02)
  plc.tx($A0)
  plc.tx($24)
  waitcnt(clkfreq*2+cnt)'wait for at least 3.5 character intervals
  GetResponse
Pub GetResponse
  repeat
    rx:=GetDataByte
    
      
PUB GetDataByte|Flag,Data,_Rx   
    
    Flag := 0                   
    repeat while Flag == 0              
      Data := plc.rxcheck  
      if Data <> -1
         _Rx := Data
         Flag := 1
     
    Result := _Rx
    debug.tx(34)      'places a " between hex characters so I can tell them apart
    debug.hex(_RX,2)  

I am reading the response fine on the parallax serial terminal.
My question is... how would I capture the response and hold it so I can parse it out later as useful data?

Many thanks in advance.

ElectricAye

You can store data on an EEPROM or record it on an SD card. Is that the kind of thing you want to do?

electromanj

No sorry I was not very clear. I can read the response from the controller, but I don't know how to "store" the response so I can work with it. Maybey I already am and don't know it? I am completely lost here. I can read the response on the serial terminal, but I would like the propeller to read the response and parse data from the response then perform an action. I hope this makes sense.

electromanj

In other projects I've done when I get data from a sensor I store it in a variable and then do something with that variable.
For instance RC time on a pot. I get the rc time decay and then compare it with a table to decipher where the pot is at.
With my current program I have figured out how to display the response from the controller on the serial terminal, but I dont know how to capture the response within the program to get info from it so the program can use that data for actions. Mostly because I'm a moron.

Mike Green

Well, you could store the response in a variable. What does the response look like?

electromanj

Hello Mike,
The resonse is actually similiar to the telegram.
For instance send: 01 03 40 9B 00 02 A0 24
recieve: 01 03 3f 00 01 C4 D4 F6

The response is not exact but that's the format.

Mike Green

You have not described a format, just given a single example of it. How about describing a pattern or structure of the byte strings?

Have a look at Extended FullDuplexSerial in the Object Exchange. It's an extension for FullDuplexSerial for receiving character strings terminated by a carriage return, but the same technique can be used for receiving other byte strings of information and processing the bytes to derive something useful.

electromanj

The protocol is modbus RTU

The message would be: 01 03 3F 29 00 02 19 D7
The response would be: 01 03 04 00 00 00 C4 FB A0

Message:
01 -slave address
03 -read register
3F, 29 -parameter to be read
00, 02- 32 bit register
19 ,D7- CRC

electromanj

I'm not 100% clear on this yet, but I think the response goes like this.

01-slave adress
03-read register
04- byte count to follow
00,00,00,C4- result of the read
FB,A0- return CRC

Ariba

You can do something like that to parse the response:

PUB GetResponse : value | cmd, bcnt, crc
  repeat until plc.rx == $01      'wait for first byte (slave address)
  cmd := plc.rx                   'get command
  bcnt := plc.rx                  'get byte count
  value := 0
  repeat bcnt                     'get value
    value := value << 8 + plc.rx
  crc := plc.rx << 8 + plc.rx     'get crc

But depending of the number of possible responds and slaves, you might need a more complex parser, and also test if the command is right.

Andy

electromanj

That worked out great! Thank you very much.

I Appriciate everyone's help!