Publication 1756-RM004B-EN-P - October 2000
MVI Backplane API 3-3
Figure 3.1 shows the relationship between the API components.
Figure 3.1 API Component Relationship
The MVI Backplane API implements a predefined configuration of the
assembly object. The configuration is shown in table 3.B.
ControlBus (Backplane)
Control Processor
(Logix 5550)
Midrange ASIC
Backplane Device
Driver
MVI API Library
Thread
Thread
Thread
CPI API Library
MVI Driver
Multi-threaded MVI Application
1756-MVI Module
(MVI56BP.EXE)
(MVI56DD.EXE)
Table 3.B - MVI API Assembly Object Implementation
Assembly Instance/
Connection Point
Max. Size (words) Connection Type Description
1
250
(1)
Class 1 Input data accessed via MVIbp_WriteInputImage
2
248
(2)
Class 1 Output data accessed via MVIbp_ReadOutputImage
5 3 Class 1 Status input (not accessible from MVI application)
6 0 Class 1 Status output (not used)
7
239
(3)
Unscheduled Message input data accessed via VIbp_SendMessage
8
239
(3)
Unscheduled
Message output data accessed via MVIbp_ReceiveMessage
(1)
The first 4 bytes are overwritten with “FF” when the connection is not open or broken (This applies only to Assembly Instance 1).
(2)
The first 4 bytes (2 words) of 250 are status words, which the MVI API strips off. (Note that the CIP API does not.)
(3)
The maximum number of words of data that can be transferred using MVI messaging will depend upon the path to the MVI module. The value shown
assumes that the controller and module are located in the same physical rack.
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