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4.3.
MESSAGE BLOCK FORMAT
Once communications have been established command messages may be sent to the Device.
Each control message starts with the STX character and ends with a checksum. The message blocks
are structured as follows:
Once communications have been established command messages may be sent to the Device.
Each control message starts with the STX character and ends with a checksum. The message blocks
are structured as follows:
STX
STX
start of message character (02 hex)
BYTE COUNT count of command message not including the STX, BYTE COUNT or CHECKSUM.
MESSAGE
variable length command message.
CHECKSUM the two's complement of the one byte sum of the MESSAGE and the BYTE COUNT.
The purpose of the checksum is to verify that all the bytes in the message that contain variable data
have been received properly. The STX is the only byte that has a fixed value, so it is the only byte not
included in the checksum calculation. The checksum is calculated by adding all the variable bytes
together. The least significant byte of this sum is then subtracted from 100 hex to compute the
checksum.
To verify that the checksum is computed correctly, add all the bytes including the
checksum but excluding the STX together. The least significant byte of the sum should be zero if the
checksum is computed correctly.
The MESSAGE consists of a command and optional bytes of data and is structured as follows:
COMMAND
single byte command directed to device.
DATA 1...DATA n variable length, any arguments required by COMMAND.
If the command message was not accepted by the Device due to a checksum error, parity error or an
invalid command the Device will respond with an NAK (05 hex) character and re-enter the SELECT
state.
If the command message is accepted by the Device and there is no data response required, it will
respond with an ACK (04 hex) character and re-enter the SELECT state.
SERIAL PROTOCOL
Model 8010TM-IRIG SDI Time Code Master with IRIG Reader Manual
BYTE COUNT
COMMAND
DATA 1
MESSAGE
.....
Revision 1.4.1
CHECKSUM
DATA n
Page 4-4
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