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Protocol Packet Definition
Packet Format
Two similar protocols are supported by CM4 software.
The original protocol with a minimum packet length of five
bytes is included for compatibility with previous software.
Additionally, a new protocol with a minimum packet length
of six bytes is included for greater robustness.
Examples of packets using both protocols are included at
the end of this book.
The format of packets using original version 1 protocol is
as follows:
receiver
start code
address
The format of packets using the new version 2 protocol
is similar:
receiver
start code
address
Start Code
Receiver Address
Transmitter Address
Length
Command
Data
Checksum
8
length
command
transmitter
length
command
address
Size: 1 byte. Always 0x40
Size: 1 byte
For responses from slave to master,
this is always 0. For inquiries from
master to slave, this must match the
slave's address as set with menu
function 3.3.1.
Size: 1 byte
For inquiries from master to slave,
this is always 0. For responses from
slave to master, this will match the
slave's address as set with menu
function 3.3.1.
Size: 1 byte
The length of the total packet
from start code to checksum.
Size: 1 byte
This is 0x28 to 0x69 as defined in
the remainder of this book.
Size: 0-250 byte(s)
This section varies according to the
command chosen and is often
empty.
Size: 1 byte
The two's complement of the sum of
all the previous bytes in the packet.
This makes the sum of the entire
packet a multiple of 0x100.
CM4 Protocol Manual
data
checksum
data
checksum
Rev. 2.4 (3/05)
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