Rockwell-automation 1771-OFE/B Analog Output Module User Manual Manuel d'utilisateur télécharger pdf (Page 46)

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When writing your program, there are some additional programming

techniques that you should consider. They are:

• block length and scaling considerations

• block transfer boundary word - PLC-2 family processors

• module update time

• buffering data - PLC-2 family processors only

• system expansion recommendations

Block Length and Scaling Considerations

There are three possible write block configurations that involve

scaling:

• no channels scaled

• fewer than four channels scaled

• all four channels scaled

No Channels Scaled

If you do not wish to scale any of your data, you can enter a block

length of five words in the write block transfer instruction. The bit

that indicates BCD or 12-bit binary data format (Bit 17) in Word 5,

the module configuration word, is the only bit in Word 5 that is

examined by the module. The remaining bits (00-16) are ignored by

the module because these bits indicate scaling value polarity and data

polarity. The module does not acknowledge negative data unless

scaling is used.

Fewer than Four Channels Scaled

To scale only one, two, or three of the four channels, enter a block

length of 00 and enter the appropriate scaling values for the channels

to be scaled. You must enter 0 or -4095 for the minimum scaling

value and +4095 for the maximum scaling value for any unscaled

channels, depending on the range selected.

Other Programming

Considerations

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Rockwell-automation 1771-OFE/B Analog Output Module User Manual Manuel d'utilisateur Page 46