Block write sizes

You can write blocks of data to processors using RSLinx Classic. The format specifiers for this are the same as they are for a block read. The major difference between the reads and the writes is that a block read (in polling mode) must be equal to or less than the maximum sizes while a block write can be any size that is valid for the processor and its file size. Therefore, while you may only read in 33 timer accumulated values with a single DDE block read, you may write up to 1000 timer preset values with a single DDE item.

Write operations may require multiple network packets. In addition, due to anomalies in some PLC-5s, any writing of timer, counter, or control word values are

all

done separately. If your DDE-compatible application wants to write 30 counter presets, 30 communication packets are required.

This table displays the maximum number of elements that can be written with a single communication packet. You can write more than the listed quantity of elements; however, if you want more than the listed quantity, use more than one communication packet. This number can not be any larger than the size possible for reading to occur. The result is a longer period of time before DDE reports back to the application that the operation succeeded or failed.

The following are special considerations for specific processors.

SLC 500 write sizes

RSLinx Classic calculates all block read sizes based on the capacity to move up to 40 words of data in a single packet. In the SLC 500 processor, you cannot write to real I/O directly. You must write to integer or binary files and write ladder logic to move these values to your real I/O.