Control Techniques Commander SE Advanced User's Manual page 11

NOTE
It is important to realise that when using group addressing (e.g. addresses 00, 10, 20 etc.), the drives within the
group addressed will not acknowledge the message sent. (If several drives try to respond at the same time, they
would all be transmitting simultaneously which is not possible when the serial link can only work with one
transmitter active at any one time.)
For security, the format of the transmitted address requires that each digit of the two-digit address is repeated, i.e. the
address of drive 23 is sent as four characters, e.g. '2 2 3 3'.
The serial address immediately follows after the first control character of the message (usually 'EOT').
Parameter characters
For transmission, all parameters are identified by four digits representing the menu and the parameter number, but without
the decimal point. Examples:
To send a message to menu 4, parameter 16, (i.e. parameter 4.16), send '0416' (the leading zero must be included)
Data characters
Data to be sent follows the characters immediately after the parameter number. The minimum length of the data field within
a message structure is one character and the maximum length is 7 characters. The data is normally expressed as a decimal
numeric value.
Block Checksum Character (BCC)
In order to ensure that the messages from or to the drive are not corrupted during transmission, the data responses are
concluded with a block checksum character (BCC). (This BCC enables the drive or host to confirm whether the data has
been corrupted or not.) See below for calculation of the BCC value depending on the data to be sent.
From all the above character types it is possible to group the correct characters together to produce valid messages. The
only two types of message are reading data and writing data. The protocol to perform these two tasks is described below.
1.3.1 Reading Data
To read a parameter value (i.e. host reading data from a drive), the message format from the host is as follows:
CC
EOT GA
Where:
CC = Control Character
GA = Group Address
UA = Unit Address
[M1][M2] = Menu number
[P1][P2] = Parameter number
NOTE
No BCC character is sent in this message.
The drive will reply with the following message structure if the 'read' message is understood:
CC
STX M1
Where:
CC = Control Character
[M1][M2] = Menu number
[P1][P2] = Parameter number
[D1][D2] ...[Dn] = Data characters including decimal point where necessary, and where:
First character: + (43 decimal or 2BH) for positive values, or
BCC = Block checksum (calculated as described below)
The data field has either 6 or 7 characters depending on whether a decimal point is transmitted.
Following a 'read' message, if the requested parameter is invalid or does not exist, the drive will reply as follows:
CC
EOT
An example of a host reading the value of parameter 1.17 on the drive that is addressed as unit 2 of group 1, the host
message is:
CC
EOT 1
The drive replies with, where [parameter 1.17] = -47.6Hz:
The BCC in this example is calculated by the drive as follows:
CC
STX 0
Commander SE Advanced User Guide
Issue Number: 4
Address
GA UA UA
Parameter
M2 P1 P2
- (45 decimal or 2DH) for negative values.
Address
1 2 2
Parameter
1 1 7 - 0
Parameter
M1 M2 P1 P2
Data
D1 D2 .... Dn
Parameter
0 1 1 7
Data
0 4 7 .
CC
ENQ
CC BCC
ETX BCC
CC
ENQ
CC BCC
6 ETX 2
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