RS-232 Remote Control Protocol
Page 5-4
Reference Guide: SM6610, SM6615, SM6620 and SM6625 Satellite Modulators
ST.RE.E10152.2
Message Definition
The Modulator replies to every message received. In all cases except for an
error, the type of the reply message is the same as the received message.
Table 5.1: Message Syntax
Start
** for messages to the Modulator, $$ for message from the Modulator
message length
The total length of the message starting from the type up to and including the checksum
type
The type of the message - detailed in the following sections
length
The length of the value
value
The data
checksum
The checksum. Calculated by adding the bytes from type to the end of value, ignoring carry, expressed
as 8-bits.
Example Message
Table 5.2 shows an example of a Message sent to the Modulator.
Table 5.2: Example Message
Byte Value Description
1 0x2A
‘*’
2 0x2A
‘*’
3
0x05
The total length of the TLV s checksum
4
0x01
The type of the message
5
0x02
The size of the value section
6
0xFE
First byte of value
7
0x12
Second byte of value
8 0x13 The
checksum
The example shown in Table 5.2 sends a message to the Modulator of type
1 containing two bytes 254 and 18.
Byte Ordering
Where multiple byte values are sent, they must be ordered with the most
significant byte first.
Message Extensions
To allow for enhancements, the receiver of the message from the
Modulator must not assume the location of the checksum, but should
calculate its location from the message length field. Doing this will allow for
the message to grow in size and still be received. If additional data is
added to a message it will be added at the end, thus allowing software
written for an earlier version of the message to still function.
