Omega DP41-B Series User Manual page 31

8. Command and Response Structure
Where "*" is the selected Recognition Character, you may select any ASCII table
symbol from "!" (hex address "21") to the right-hand brace (hex "7D") except for the
caret "^", "A", "E", which are reserved for bus format request.
"[nn]" are the two ASCII characters for the device Bus Address. Use values from "00" to
hex "C7" (199 decimal).
"ccc" stands for the HEX-ASCII COMMAND CLASS letter (one of twelve given in
Table 8.1), followed by the two HEX-ASCII COMMAND SUFFIX characters identifying
the meter data, features or menu items to which the command is directed (given in
Table 8.2).
"<data>" is the string of characters containing the variable information the computer is
sending to the meter. These data (whether BCD or binary) are encoded into
HEX-ASCII characters, two characters to the byte, except for the "Y01", "write to the
display" command: here, the desired display upper-case letters, numbers or (limited)
symbols are transmitted by plain ASCII characters. Square brackets (indicating optional
status) enclose this <data> string, since some commands contain no data.
"[hh]" is the optional CHECKSUM BYTE, two HEX-ASCII characters equal to the
modulo 256 sum of all the preceding bytes including the serial recognition character.
Each addition to this sum uses the ASCII 7 bits plus the parity bit as the most-
significant bit. Any carry (overflow) bits are discarded. The checksum is transmitted
most-significant character first.
Message errors can be discovered by computing the checksum from the received
bytes and comparing that total with the transmitted checksum. However, most systems
have a good signal-to-noise ratio, so that checksum errors are rare and the procedure
is infrequently used.
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