55xGenComm1_29
11
Exception response message
Byte Field
name
Notes
0 Slave
address
1
Function code +128 (131)
Top bit is set
2
Exception code
1 - Illegal function code
2 - Illegal data address
6 - Slave device busy
3 –4
Error check CRC
Unimplemented register and field values
Size of register
Value returned
Notes
1 bit flag within a register
0
No third state exists for a flag to indicate
it is not valid
2 bit named digital
input/output code
3 Unimplemented
input/output
4 bit alarm condition codes
0xF
Unimplemented alarm
4 bit LED colour code
0xF
Unimplemented LED
16 bit unsigned, any scale
0xFFFF
The largest number
16 bit signed, any scale
0x7FFF
The largest positive number
32 bit unsigned, any scale
0xFFFFFFFF
The largest number
32 bit signed, any scale
0x7FFFFFFF
The largest positive number
ASCII strings
“ ”
A string of spaces (Unicode 0x0020),
NULL terminators are not used
Unicode strings
“ ”
A string of spaces (Unicode 0x0020),
NULL terminators are not used