8-6
VersaPoint™ I/O System Profibus-DP NIU User’s Manual – August 2005
GFK-1911B
8
Request and Response Format
The format for all types of access (Request and Response, Read and Write) in
DP/V1 is:
<DP/V1 header> <Data (PCP/DP/V1)>
The format of the DP/V1 header is always:
<DP/V1 service> <Slot> <DP/V1 index> <DP/V1 length>
The <Data (PCP/DP/V1)> is optional depending on the service. It has the following
structure:
Access
Service
Data
Request
Object data
Write objects
(NIU)
Response
None
Request
None
Read objects
(NIU)
Response Object
data
Write request (Write)
Write PCP/Index high/Index low/Subindex/Length of PCP
data/x bytes of PCP object data
Write response (Write)
None
Read request (Write)
None
Write objects
(I/O modules)
Read response (Write)
PCP acknowledgment
Write request (Read)
Read PCP/Index high/Index low/Subindex
Write response (Read)
None
Read request (Read)
None
Read objects
(I/O modules)
Read response (Read)
PCP acknowledgment
Write request (Write)
Invoke ID/Write PCP/Reserved/Reserved/ Reserved/
Reserved/Index high/Index low/ Reserved/Subindex/
Reserved/Length of PCP data/x bytes of PCP object data
Write response (Write)
None
Read request (Write)
None
Write objects
with Invoke ID
Read response (Write)
Invoke ID (mirrored)/Write PCP/ Reserved/ Reserved
Write request (Read)
Invoke ID/Read PCP/Reserved/Reserved/ Reserved/
Reserved/Index high/Index low/ Reserved/Subindex
Write response (Read)
None
Read request (Read)
None
Read objects
with Invoke ID
Read response (Read)
Invoke ID (mirrored)/Read PCP/Reserved/ Reserved/
Reserved/Length of PCP data/
x bytes of PCP object data
In the event of a faulty response, the format is:
▪
For a DP/V1 error:
<DP/V1 service> <Error decode> <Error code 1> <Error code 2>
1. For an I/O module error:
<DP_V1 service> <Slot> <DP_V1 index> <DP_V1 length> <Error data (PCP_DP_V1)>
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