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4.1.3. Message Block Format
The MESSAGE consists of two command bytes followed by optional bytes of data, followed by a
checksum and is structured as follows:
CMD 1/CNT
CMD1/CNT
First byte of the command. The upper nibble is the command prefix and the lower nibble
is the number of bytes of data.
CMD2
Second byte of the command.
DATA 1...DATA n
CHECKSUM The one byte sum of the CMD1/CNT, CMD2 and DATA bytes.
calculated on the actual bytes of the command not the ASCII Hex representation of
these bytes.
The purpose of the checksum is to verify that all the bytes in the message that contain variable data
have been received properly. The checksum is calculated by adding all the previous bytes together.
The least significant byte of this sum is then used as the checksum.
For example, to request the current time code data from the VTR, the command message would be
transmitted as follows:
If the VTR does not accept the command message due to a checksum error, parity error or an invalid
command, the VTR will respond with an NAK response (11H, 12H).
If the VTR accepts the command message and there is no data response required it will respond with
an ACK response (10H, 01H).
If the command message requires a data response, the VTR will transmit a response message that
consists of two command bytes followed by optional bytes of data, followed by a checksum and is
structured as follows:
RSP 1/CNT
RSP1/CNT
First byte of the response. The upper nibble is the response prefix and the lower nibble
is the number of bytes of data.
RSP2
Second byte of the response.
DATA 1...DATA n
CHECKSUM The one byte sum of the RSP1, RSP2 and DATA bytes. The checksum is calculated on
the actual bytes of the response not the ASCII Hex representation of these bytes.
If the current LTC reader time code was 12:45:30:00 Non Drop Frame the response message would be
received as follows:
7
4
RSP1
CNT
SERIAL PROTOCOL
CMD 2
DATA 1
variable length, any arguments required by the command.
6
1
CMD1
CNT
RSP 2
DATA 1
variable length, any data required by the response.
0
4
0
0
RSP2
10
1
FRMS
FRMS
Model 8010-SIE Digital Source ID Encoder Manual
.....
0
C
CMD 2
.....
3
0
4
10 SEC 1 SEC 10 MIN 1 MIN 10 HR 1 HR
Revision 2.2
DATA n
CHECKSUM
The checksum is
6
D
CHECKSUM
DATA n
CHECKSUM
5
1
2
F
CHKSUM
F
Page 4-2
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