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CHAPTER 8 ANALOG I/O

RPC-2300 Page 23

channel 0 would use J7 pin numbers 1 and 3.

Single ended inputs 2-7 are available.

input specifies single ended or differential. 0 =

differential, 1 = single ended.

range is voltage input. 0 = ±5V and 1 = 0 to + 5V.

Below are sample syntaxes for the CON FIG AIN

command:

1. Single ended mode, 0-5V input

CONFIG AIN chan,1,1

The input voltage is from 0 to 5 volts. The result from

the AIN function is 0 for 0.000V and 4095 for

+ 4.9988V. chan may range from 0 to 7, if no other

channels are used for differential inputs.

2. Differential mode, 0 to + 5V input

CONFIG AIN chan,0,1

chan can be 0, 2, 4, or 6. The input may range from 0

to + 5V. However, if the (-) input is more positive than

the (+ ) input, the result w ill always be zero. The result

from the AIN function is 0 for a difference of 0.000V

and 4095 for a difference of 4.9988V.

3. Single ended, ±5V input

CONFIG AIN chan,1,0

The input ranges from -5V to + 5V. The r esult from an

AIN function is 0 for -5.000V, 2048 for 0. 000V, and

4095 for + 4.9988V.

4. Differential, ±5V input

CONFIG AIN chan,0,0

The input ranges from -5V to + 5V. T he result is the

difference of the two voltages. AIN will return 0 for a

difference of -5.000V, 2048 for a difference of 0.000V,

and 4095 for a difference of 4.9988V.

ACQUIRING ANALOG DATA

Once the analog input is initialized, the AIN function is

used to acquire data. The syntax is:

S = AIN(ch)

Where: ch = channel number, 0-7

This command reads the voltage and returns a number

from 0 to 4095 to the variable S. The number returned

corresponds to the voltage input and the type the channel

was configured for.

To convert the returned numbers to a voltage, use the

following formulas:

5V Unipolar: A = 0.0 0122 * AIN(chan nel)

±5 Bipolar: A = 0.00244 * AIN (channel) - 5

The AIN function requir es about 1 m s to convert a

channel of data. Additional time is needed to store the

data. Saving data to a single dimension array takes 500

micro-seconds longer than saving to a simple variable.

Datalogging on a timer tick

Some application require that data be taken at fixed

intervals. The ON TICK construct can be used to take

data in intervals from 0.01 to 655.35 seconds. The

program below takes 100 samples on 2 channels every

10 seconds.

10 DIM F(100,2)

20 ON TICK 10 GOSUB 50

30 ..this is a dummy loop

40 GOTO 30

50 F(I,0) = AIN(0)

60 F(I,1) = AIN(1)

70 INC I

80 IF I = 100 THEN ON TICK 10 GOSUB

90 RETURN

Line 80 shuts off interrupts after 100 samples.

MEASURING HIGHER VOLTAGES

Input voltages higher than 5V are measured by placing a

resistor in series with the input. Use the following

formula to determine the required series resistance:

Rs = Vi * 20,000 - 100, 000

Rs is the resistor value in ohms in ser ies with the input.

Vi is the maximum input voltage. If the result of your

calculation is 0 or negative, a series resistor is not

necessary.

NOTE: If an input voltage exceeds + 5.0V or is less

than -5.0V, other channels will be in error.

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