DTL_RMW comments

The DTL_RMW and DTL_RMW_CB functions have a limit of 40 concurrent asynchronous read/write operations.

The DTL_RMW function performs read, modify, and write operations on the specified data item. It sends an AND-mask and OR-mask to the target processor where they are applied to the contents of the data item in one uninterruptable operation.

For PLC-3 and PLC-5/250 stations, the data item must have a PLC station data type of LONG, WORD, or UWORD and must consist of only one element. For PLC-5 stations, the data item must have a PLC station data type of WORD, or UWORD and must consist of only one element. This operation cannot be performed on entire structures, Block Transfer data items, bits, bitfields, or data items whose client data type or PLC station data type if floating-point.

The AND mask and OR mask, provided as longword values by the client, are checked to ensure they are consistent with the data item's application data type (LONG, WORD, UWORD, or RAW).

For PLC-5/250 station access only: The original value of the data item, before application of the AND and OR masks, is copied to a buffer provided by the client. The original value will be converted (if necessary) according to the application data type of the data item.

For PLC-3 and PLC-5 stations: The original value is not returned to the client; only the final completion status is provided.

The final I/O completion status code (

io_stat

) may be any of the return values previously listed.

This function has the following restrictions: