IW or PIW ?

[panthripu]

hi
when using some analog input connect at say xxx input ,what sould i use in program ? IWxxx or PIWxxx.similarly after unscaling what to be used to transfer output at output channel ? QWxxx or PQWxxx.

 

[godfrey]

Analog inputs are PIW and analog outputs are PQW. PIW stands for peripheral input word and PQW stands for peripheral output word.

 

[Labotomi]

Peripheral inputs use a separate memory area. To use the values from an analog input you will have to use the PIWxxx address. The IWxxx address uses a separate memory area which is not associated with the peripheral area.

You'll probably want to use a scaling block unless you want the raw data from the analog input. The resulting value from the scaling block will be assigned an address which can be used for your logic.

To use analog outputs, you commonly use an unscale block to get the value back to the raw format used by an analog output cards and address it as PQWxxx.

 

[panthripu]

iw or piw

then where iw and qw are used ?

 

[RRobbins]

Labotomi was close. The PIW is read any time you request it in your program. Same with PQW. If you were using STL programing and had L PIW XXX T MW 100, The processor would go out and read the input BEFORE the next instruction. At the end of the cyclic scan the processor writes ALL if the QW's to the PQW's and the reads the PIW's and copies them to the IW's. That area is called the Proces Image Table. Your logic is normally done using I 0.0. Q 3.2, etc. The PIWs and PQW's can only be read or wrote as bytes, words and double words. (PIB, PIW, PID) If you call a PIW or PQW that don't exist, your ptocessor will fault, with IW's it wont. IW's can be addressed to a fixed level, determined by your processor. On smaller 300's it's usually 128, some 300s and 400s it can be 512, some 400s 1024, etc. above that you have to use PIW or PQW. If you use that area for I/O, then you would have to load the PIW and tranfer it to a MW to examine an individual bit.