Experimental Physics and
Industrial Control System

Hello,

My name is Kyle, and I am working on an EPICS driver for an Agilent Technologies TwisTorr 304 Controller. Unfortunately, I have hit a bit of a roadblock in my protocol file, and I need a little nudge in the right direction. I am able to send the device commands and receive responses, but I am looking to automate the checksum process with some of the built in checksum converters. Could you please teach me how to use the converters and flags to ignore the first byte and compute the checksum of any given input and output? 

The Checksum Calculation

#The MESSAGE is a string with the following format:

#<STX>+<ADDR>+<WIN>+<COM>+<DATA>+<ETX>+<CRC>

#<CRC> = XOR of all characters subsequent to <STX> and including the <ETX> terminator. The value is hexadecimal coded and indicated by two ASCII character.

# Example for Soft Start (ON) COMMAND
# <0x02>|<0x80>|<0x31><0x30><0x30>|<0x31>|<0x31>|<0x03>|<0x42><0x32>|
#   STX   | ADDR |              WINDOW        |  WR     |    ON  |   ETX   |           CRC       |

# Response for Soft Start (ON) COMMAND
# <0x02>|<0x80>|<0x06>|<0x03>|<0x38><0x35>|
#   STX    | ADDR |  ACK |  ETX    |         CRC        |

The bytes for the checksum begin with ADDR and end with EXT (inclusive). The resulting checksum is B2 in hex. It is indicated by two separate ASCII characters. 'B' = 42 and '2' = 32. This is for the Soft Start (ON) command. The same logic would apply to the response.

My Protocol File

Terminator = "";
ExtraInput = Ignore;
LockTimeout = 2000;
ReplyTimeout = 100;
WriteTimeout = 50;
ReadTimeout = 50;

#Requests and Answers

#Command that turns on the soft start function

softStartOn {
    out "\x02\x80\x31\x30\x30\x31\x31\x03\x42\x32";
    in "%s";
}

I would like to know how to use %<xor> properly in this command to calculate the checksum. My attempts are listed below:

\x02\x80\x31\x30\x30\x31\x31\x03\%<xor>

\x02\x80\x31\x30\x30\x31\x31\x03\%1.1<xor>

\x02\x80\x31\x30\x30\x31\x31\x03\%2r<xor>

\x02\x80\x31\x30\x30\x31\x31\x03\%2R<xor>

\x02\x80\x31\x30\x30\x31\x31\x03\%xor

\x02\x80\x31\x30\x30\x31\x31\x03\%1.12R<xor>

\x02\x80\x31\x30\x30\x31\x31\x03\%2r%<xor>

The response to the command is 02 80 06 85 (an ACK). My attempts leave me with 02 80 15 96 (a NACK). I am using this example as a means of debugging.

Thank you for your help,

Kyle