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2408
f
& 2404
f
PROFIBUS Communications Handbook Demand Data
2408
f
and 2404
f
PROFIBUS Communications Handbook 7-3
THE COMMAND CODE AND TAG ARE ENCODED INTO REGISTER 1 AS FOLLOWS:
Bits 15-12 Bit 11 Bit 10 - 0
Command Code Reserved Parameter Tag
Because only 11 bits are available for the Parameter Tag, the maximum tag allowable for standard demand data operations is
2048. The 2400
f
series controller allows tag values of up to 16383, therefore, extended tags have been provided using register
2. This is particularly important if ramp/dwell programs or configuration information is to be transferred over PROFIBUS-DP.
Fields in a request (output registers) should be set as follows: NB: Eurotherm Extensions are printed in bold italic text
Command (Hex) Request (Master to Slave) Parameter Tag Extended
Parameter Tag
Value
0
000
No Command - - -
1
000
Read Request Tag to Read - -
2
000
Write Request Tag to Write - Value to write
3
000
Extended Read Request Must be Zero Tag to Read -
4
000
Extended Write Request Must be Zero Tag to Write Value to Write
Valid responses to a given command are as follows:
Command
Field in request
(output register)
Command
Field in response
(input register)
Meaning Returned Value
(input register 4)
0
000
0
000
Acknowledge No Command -
1
000
1
000
Tag Read Successfully Value Read
1
000
7
000
Tag Read Not Successful Error Code (see below)
2
000
1
000
Tag Written Successfully -
2
000
7
000
Tag Write Not Successful Write Request
3
000
1
000
Extended Tag Read Successfully Value Read
3
000
7
000
Extended Tag Read Not Successful Error Code
(see below)
4
000
1
000
Extended Tag Written Successfully -
4
000
7
000
Extended Tag Write Not Successful Error Code
(see below)
The command field in the response message either
• Confirms that no operation has been requested
• Indicates that a Read or Write request has been completed successfully
• Indicates that a Read or Write has failed.
Error Codes in input register 4 are as follows.
Error Code Meaning
0 Invalid Tag Number
1 Read Only Parameter
2 Value out of range