6-20 Settings Date Code 20010518
SEL-2020 Instruction Manual
specify the number of bytes that follow the item being specified. To specify a byte index, you
enter a positive integer. To specify a character you can enter the character or, if the character is
non-printable, the ASCII character code. Add the trailing ‘i’ to specify inclusion of the character
itself. You must quote any numeric character so that it is not treated as a byte index (e.g., enter
‘9’ or “9” to indicate the character 9 as opposed to byte 9). The examples in Table 6.6
demonstrate the use of each method.
Table 6.6: Example Position Settings
Example
Setting
Meaning
START1=1 start calculating checksum at first received byte
START1=# start calculating checksum at the first byte following the character ‘#’
START1=#i start calculating checksum at the ‘#’ character (‘#’ is included in checksum).
START1 = E10 start calculating checksum 10 bytes before the end of the message
STOP1 = 20 stop checksum calculation at 20th byte (byte 20 is the last byte of data)
STOP1 = \003 stop checksum calculation at ETX character (03 character code)
STOP1 = \003i stop checksum calculation after ETX (ETX character is included in checksum)
STOP1=E4 stop calculating checksum 4 bytes before the end of the message
CHKPOS1 = 40 the checksum starts at the 40th byte of the received data.
CHKPOS1=\001 the checksum starts after the SOH character (01 character code).
CHKPOS1=E2 the checksum is located 2 bytes from the end of the message
Suppose the string below will be sent to the SEL-2020 and you wish to verify that there are no
transmission errors. Assume that the checksum is calculated on the data within the quotes. In
this case the checksum is a 16-bit checksum in ASCII hexadecimal format with the high byte
first. There are many different ways that you could specify the locations of the data and
checksum. Four examples are given.
received data: “This is data”,044E
settings:
CHECK = 16A,
ORDER = H,
method 1: START = 2, STOP = 13, CHKPOS = 16
method 2: START = E18, STOP = E6, CHKPOS = E4
method 3: START = “, STOP = “, CHKPOS = ‘ ,’
method 4: START = 2, STOP = “, CHKPOS = E4
The method you choose for each of the position settings will depend on the format of the
received data. These position settings apply only to the data to be stored. This means that the
NUMn setting must be large enough to contain all of the data and the checksum. Otherwise the
checksum verification will consistently fail. The position settings must be sequential in the
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