Writing The Control Program - Automation Direct DL405 User Manual

11–10
D4-02DA 2-Channel Analog Output

Writing the Control Program

Update Either
Channel
Calculating the
Digital Value
As mentioned earlier, you can update either channel or both channels during the
same scan. Since the module does not have any channel select bits, you just simply
determine the location of the data word and send the data word to the output module
whenever you need to update the data.
V40502
MSB
Unused
Channel 2
Your program has to calculate the digital
value to send to the analog module.
There are many ways to do this, but most
all applications are understood more
easily if you use measurements in
engineering units. This is accomplished
by using the conversion formula shown.
You may have to make adjustments to
the formula depending on the scale you
choose for the engineering units.
Consider the following example which controls pressure from 0.0 to 99.9 PSI. By
using the formula, you can easily determine the digital value that should be sent to
the module. The example shows the conversion required to yield 49.4 PSI. Notice
the formula uses a multiplier of 10. This is because the decimal portion of 49.4
cannot be loaded, so you adjust the formula to compensate for it.
4095
A + 10U
10(H * L)
4095
A + 494
1000 * 0
A + 2023
D4–02DA
8pt 8pt 32pt
Output Output Output
Y0 Y10 Y20
– – –
Y7 Y17 Y57
V40500
LSB MSB
Data Bits Unused
A + U 4095
A = Analog value (0 – 4095)
U = Engineering units
H = High limit of the
L = Low limit of the engineering
16pt 16pt 16pt
Output Input Input
Y60
–
Y77
V40503
V40501
Data Bits
Channel 1
H * L
engineering unit range
unit range
LSB