7.4 Using Change of Value Reads
If it is necessary to acquire updated data quickly from a system that has a large number of points then RCOV is the most
effective method to do this. The PSP Server will return the first data block that has been updated.
From Host CPU:RCOV<cr>
Response from ProtoCessor:RD-NA:data,OF:x,VA:y<cr>
Where:data-> is the data array name.
x-> offset within that data array.
y-> value of the data.
The format of the data returned will be the basic data type of that point on the server.
In order for the PSP server to know that this RCOV arrived at the client correctly the client needs to send an
acknowledgement.
From Host CPU:A<cr> or :ACK<cr>
Response from ProtoCessor:No response from ProtoCessor, waits for next message.
This then clears the COV flag for that particular piece of data.
The host CPU can also ACK the data with an RCOVA:
From Host CPU:RCOVA<cr>
Response from ProtoCessor:RD-NA:data,OF:x,VA:y<cr>
As well as clearing the (now read) COV flag this also allows the server to respond with the next piece of updated data that it
finds. If the server cannot find any further updated data, it will respond with an OK, which signals to the client that all the
updated data has been read. The client can then resume normal RCOV polls until it, once again, receives updated data.
From Host CPU:RCOVA<cr>
Response from ProtoCessor:OK<cr>
23 ProtoCessor Design Guide
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