7I76 28
REFERENCE INFORMATION
SSLBP
PROCESS DATA DISCOVERY
The SSLBP interface provides information to allow the host to determine the name,
number, units, sizes, types, directions, and scaling of process data elements. This
information is read from the remote device via a setup mode start followed by a series of
remote read operations.
Note to the bewildered: process data discovery and its complications are not
needed to access the 7I76 via SSLBP. In fact the 7I76's data can be accessed via SSLBP
with no more than a few register reads and writes The sole purpose of process data
discovery is to allow the driver to present nicely named and formatted data to the host
without the driver having any built in knowledge of the remote device.
PROCESS TABLE OF CONTENTS
After a normal start or setup start command, the PTOCP word in the low word of
interface register 2 is a pointer to the current process table of contents (PTOC) in the
remote device.
If remote devices that do not support process device discovery are present, their
PTOCP will be 0, and process data organization must be inferred from the remote device
name.
Remote reads from this location will return the first entry in the PTOC. All PTOC
entries are pointers with a size of 2 bytes. The end of the PTOC is marked with a 0
sentinel. Each PTOC entry points to a process data descriptor. Here is an example of a
5 entry PTOC (PDD is Process Data Descriptor)
ENTRY ADDRESS CONTENTS
0 PTOCP POINTER TO PDD 0
1 PTOCP+2 POINTER TO PDD 1
2 PTOCP+4 POINTER TO PDD 2
3 PTOCP+6 POINTER TO PDD 3
4 PTOCP+8 POINTER TO PDD 4
5 PTOCP+10 0x0000 (END OF TABLE)
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