6-4 The Message Format
Normal Response Message
The normal response message contains the same slave address and function code as the
command message, indicating to the master, which slave is responding and to what type of function
it is responding.
The number of data bytes is the number of data bytes returned in the response message. The
number of data bytes is actually the quantity (in the command message) multiplied by 2, since
there are two bytes of data in each register.
The data section of the response message contains 8 upper and 8 lower bits of data for each
register that has been read from the drive.
A CRC-16 value is generated from a calculation using the values of the address, function code,
number of data bytes, and register data sections of the message. The procedure for calculating a
CRC-16 value is presented at the end of this chapter. When the master receives the response
message, it calculates a CRC-16 value and compares it to the one in the CRC-16 field of the
response message. If these two CRC-16 values are the same the master has received the proper
response message.
The starting register, 20h
(Status Signal), has a value of
4. (Drive Ready)
02h
SLAVE ADDRESS
FUNCTION CODE
03h
00h
04h
START-
ING
REGISTER
CONTENTS
UPPER
LOWER
NO. OF DATA
BYTES
08h
NEXT
REGISTER
CONTENTS
00h
00h
UPPER
LOWER
NEXT
REGISTER
CONTENTS
00h
00h
UPPER
LOWER
NEXT
REGISTER
CONTENTS
17h
70h
UPPER
LOWER
CRC-16
ACh
1C
h
LOWER
UPPER
The next register, 21h
(Drive Fault Content), has
a value of 0 (no drive
faults).
The next register, 22h
(Communication Data Link
Status), has a value of 0 (no
communication errors).
The next register, 23h
(Frequency Reference),
has a value of 1770h or
6000 dec. (60.00 Hz).
