Rockwell Automation MD65 Profibus Communication Card - Manual (Page 92)

D-6 PROFIBUS Communications Module
This circuit utilizes the Param eter Protocol. A REQUEST to Station 2 is processed only one at a time, and after each
RESPONSE from Station 2 a zero must be sent and received to 'handshake' before the next REQUEST/RESPONSE
transaction can take place. For example:
Send a parameter read request --> Receive a param. read response --> Send a "0" --> Receive a "0" --> [Transaction compl.]
If the RESPONSE PCA Word 1 (N10:8) is "0", then a REQUEST can be initiated.
Elsewhere in the user program these words must be loaded with message data prior to initiating the REQUEST.
N7:30 = RC = the operation to be performed ("1" = Read, "2" = 16-bit Write)
N7:31 = PNU = the parameter number to read or write
N7:32
N7:33 = PVA #1 (the parameter value (high word)) - only used when writing parameters
N7:34 = PVA #2 (the parameter value (low word)) - only used when writing parameters
The four Parameter Protocol Words set up in the scanner are used to perform the Parameter Protocol:
N20:8 = contains RC (the operation to be performed) and PNU (the parameter number to read or write) combined
N20:9 = Subindex (the MDIport #)
N20:10 = PVA #1 (the parameter value (high word))
N20:11 = PVA #2 (the parameter value (low word))
B3:19/0 is turned ON elsewhere in the program after a REQUEST message (N7:30-34) is loaded. This causes one
Parameter Protocol read or write to occur and B3:19/0 is turned OFF when the transaction is complete.
11
B3:19
0
Station 2
Par Prot
Messaging
Request
EQU
Equal
Source A N10:8
0<
Source B 0
0<
EQU
Station 2
RESPONSE
PCA Word
MOV
Move
Source N7:31
77<
Dest N20:8
0<
MOV
Station 2
PCA Word
N7:30
0
RCbit 0
L
N20:8
12
PCA Word
RC bit 0
N7:30
1
RCbit 1
L
N20:8
13
PCA Word
RCbit 1
N7:30
2
RCbit 2
L
N20:8
14
PCA Word
RCbit 2
COP
Copy File
Source #N7:32
Dest #N20:9
Length 3
COP
IND Word
(Subindex)
= SubIndex = the MDI port # ("0" = Host or MD65 drive, "5" = MDCOMM-PBUS, etc.)
N10:8 is the Station 2 Response Parameter Access Word 1. It is <> 0 when a message has been received in response to a
message request. If the response is >= 7000 hex (28672 decimal), then the adapter is responding that an error has occured.
In this case, the returned data in the response will contain a fault code and not the parameter value data.
The response message can be found at:
N7:40 = PCA Word = contains RC and PNU
N7:41
N7:42 = PVA #1 = the parameter value (high word)
N7:43 = PVA #2 = the parameter value (low word)
The PVA's will either contain parameter read data, echo the parameter write data or contain an error code if unsuccessful.
12
B3:19
0
Station 2
Par Prot
Messaging
Request
NEQ
Not Equal
Source A N10:8
0<
Source B 0
0<
NEQ
Station 2
RESPONSE
PCA Word
COP
Copy File
Source #N10:8
Dest #N7:40
Length 4
COP
RESPONSE Message
PCA Word
MOV
Move
Source 0
0<
Dest N20:8
0<
MOV
Station 2
PCA Word
U
B3:19
0
Station 2
Par Prot
Messaging
Request
13 END
= Subindex = the MDI port # ("0" = Host or MD65 Drive, "5" = MDCOMM-PBUS, etc.)