Rockwell Automation 1771-OFE/B Analog Output Module User Manual - Manual (Page 46)

4-10
Publication 1771Ć6.5.30 - November 1998
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