Rockwell Automation 1785-Vx0B, D17856.5.9 PLC-5 VME VMEbus Programmable Controllers User Manual - Manual (Page 106)

7 Chapter
7-1
Performance and Operation
Read this chapter to learn about the performance and theory of operations
of the PLC-5/VME processor.
The PLC-5/VME is a standard PLC-5 processor with an embedded VME
coprocessor that uses standard port 3A for coprocessor communication.
The embedded VME coprocessor:
handles any VME ladder-logic message instructions
serves the continuous-to/from-copy function in the PLC processor
maintains the VME status file in the PLC processor
handles all host VME processor requests for communication to the
PLC processor
All message instructions from the PLC processor going to the VMEbus are
processed like other message instructions in the PLC processor. The
control bits act exactly the same way. Once the VME coprocessor gets the
command, it processes it according to the function.
For a VME write instruction (CTV), the coprocessor makes another
request back to the PLC processor to get the data being sent to the
VMEbus. It arbitrates for the bus if necessary and then transfers the data.
After the last DTACK from the VMEbus, it sends a command back to the
PLC processor to let it know the command completed; and then the done
bit is set for the message instruction.
For a VME read instruction (CFV), the coprocessor arbitrates for the
VMEbus and fetches the data. It sends the data to the PLC processor and
then tells the PLC processor that it is completed.
For the send VME interrupt, the coprocessor gets the command along with
the interrupt level and status ID code. It generates the VMEbus interrupt
and waits for the interrupt-acknowledge signal on the VME backplane.
When it sees this signal, it puts the status ID on the backplane along with
DTACK for the interrupt handler. It then sends a command back to the
PLC processor to let it know of completion so that it can set the done bit to
the message instruction.
Chapter Objectives
VME Throughput Time