SlotServer Configuration Manual
Page 30 of 37
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Appendix D.
REFERENCE
Appendix D.1.
Description of Data Transfer Process
The data connection from the SlotServer to the Logix CPU consists of 496 bytes of input and 496 bytes of output
data. Of the 2 Map Descriptors specified, the one with the WRBC function writes data to the Logix CPU filling its
input data, and the one with the RDBC function accepts the Logix CPU’s output data.
The Map Descriptor’s IO_Data_Type field organizes the 496 bytes into either Bytes (SINT), Words (INT) or Double
Words (DINT or REAL) reducing the number of elements that can be transferred. Of the resulting number of
elements, the first 4 are reserved for the IO image header (Refer to Appendix D.2).
The SlotServer acts as a multiplexer when it sends data to the Logix-CPU and as a demultiplexer when it receives
data from the Logix-CPU.
The diagram on the next page describes the SlotServer operation methodology:
For input data, the input data from the external device is placed into the 25 Data Arrays numbered In_1 to In_25.
The SlotServer sends the data from these Data Arrays over the IO image connection one at a time by placing the
block number at offset 2 of the image header and the data from offset 4. The reverse happens at the Logix-CPU
where a demultiplexer is implemented in Ladder to route the data to each of the 25 CPU Tags.
For output data, the Logix-CPU has to place the data and block number into the Output Image Tag and send it to
the SlotServer. The SlotServer then demultiplexes the data by placing it into the appropriate Out_x Data Array
depending on the block number specified in the IO image header.
