User guide

5 - 22

PN 074-566-P1B

Composer Elite Operating Manual

5.5.1 Command

This section describes the command format.

See section 5.6, Communication Commands, on page 5-27 for details on specific

command IDs.

The message received by Composer Elite contains a data packet preceded by a

length and terminated by a checksum.

Composer Elite will always send a response to any command it receives.

5.5.1.1 Command Packet (Host to Composer Elite Message)

Length . . . . . . . . . . . . . . . . . . . . . . . 2 bytes Low / High (not including checksum

or length bytes). Numeric value representing

the number of characters in the command. In

order of transmission, the low byte will

precede the high byte. Normally, the number

for characters will be less than 9. In this case,

the low byte will contain the character count

while the high byte will have zero value.

Message . . . . . . . . . . . . . . . . . . . . . <Command>

Checksum . . . . . . . . . . . . . . . . . . . . 1 byte, sum, modulo 256, of all bytes, not

including length. Modulo 256 is the numeric

value from 0 to 255 representing the modulo

256 remainder of the sum of the values of the

ASCII codes that comprise the command.

5.5.2 Response

This section describes the response format that is returned in the data field of the

response message. See section 5.6, Communication Commands, on page 5-27 for

more details on responses. The message sent by Composer Elite contains a data

packet preceded by a length and terminated by a checksum. See section 5.5.2.1

for a detailed description of the received message structure.

If a command generates an error in response, an error code is returned (see

section 5.5.2.2) in the Response Message and the SS bit in the status byte (see

Table 5-18 on page 5-24) is set to 0. The SS bit is set to 1 indicating successful

completion of the received command.