Command Packet Format - Siemens SITRANS RD200 Operating Instructions Manual

Command Packet Format

SOH Meter
(0x01) Address
1. SOH (0x01) - Unconditional start of message character. Valid any time except while a
reply is in progress.
2. Two character meter address code (00 - 99).
3. Two character command code.
4. Data or argument field(s) if required.
5. Two character ASCII hex checksum (0x00 – 0xFF) which represents the 8 bit result of
the negative of the sum of all data characters in the command code and data fields.
Parity bits are excluded from the calculation.
Checksum = 1 + not(Command Code[high] +
6. ETX (0x03) - Terminator character.
Example: Read the set point for Relay #1 of meter 00:
Address: 00
Command Code: 26
Arguments: "S0" . 'S' = Set point; '0' = Relay #1 (relay numbering starts with 0)
Checksum = 1 + not('2' + '6' + 'S' + '0')
Therefore, the complete command packet that is sent = 0x01, "0026S015" , 0x03
In hex form = 0x01 0x30 0x30 0x32 0x36 0x53 0x30 0x31 0x35 0x03
7ML19985JS01
Comm Comm
Meter
and and
Address
Code Code
Command Code[low] + any data or arguments)
= 1 + not(0x32 + 0x36 + 0x53 + 0x30)
= 1 + not(0xEB)
= 1 + 0x14
= 0x15
SITRANS RD200 – OPERATING INSTRUCTIONS
Data
Check- Check-
(as
sum sum
reqd.)
ETX
(0x03)
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