User Manual - JVL Industri Elektronik A/S

3.14 RS232 Interface
3.14.5 Synchronisation
During communication with the Controller, each command string must be terminated
either by a (ASCII 13) or a semi-colon “;”. This tells the Controller that the
command string is complete and interpretation can begin. When a checksum is used,
command interpretation will not begin until the entire command line has been received,
i.e. is terminated by a . A maximum of 80 characters may be sent in a single
command line.
If the Controller is set to use addressing (ADDR>0), the string can be terminated by "; ;"
3.14.6 Checksum
In industrial applications, electrical noise from motors, etc., often occurs. This noise is
quite arbitrary and random and cannot be eliminated 100% even by effective electrical
filtering. To ensure correct transmission of Controller commands therefore, a checksum
can be used. A typical command line may be as follows:
25KP=25;KI=471d
Address
Command no. 1
Delimiter
Command no. 2
TT0037GB
Checksum
In this example, addressing is used (address 25). Two commands, delimited by a semicolon
“;”, are transmitted followed by a checksum. The checksum consists of two characters.
The checksum is a ‘simple’ checksum and is calculated in the following way:
First the ASCII value of each of the characters in the command line is determined. These
values are summed and the two least significant characters (the least significant byte) of
the result’s hexadecimal value are used.
The two least significant digits are converted to ASCII values and transmitted along with
the command line. The actual calculation in this example is as follow:
50+53+75+80+61+50+53+59+75+73+61+52+55 = 797 (decimal) = 31d (hexadecimal)
The checksum is thus 1d which is sent as ASCII 49 (decimal) and 100 (decimal). The
hex.characters a-f can also be sent as capitals, i.e. d can also be sent as ASCII 68 (decimal).
In the event that the command string is corrupted during transmission, the checksum will
not correspond and the Controller will report an error message “E9”, indicating that a
checksum error has occurred. The command string must then be re-transmitted. The
checksum function is activated using the CHS command.
JVL Industri Elektronik A/S - User Manual - AC servocontroller AMC10/11/12 39