Remote-processing RPC-2350 Instrukcja Użytkownika Pobierz pdf (Strona 44)

ANALOG I/O CHAPTER 8

8-2

Initializing Inputs

The RPC-2350 can have up to eight single-ended inputs,

four differential, or a mixture of single ended and

differential inputs. On a reset, inputs are configured for

0-5V, single ended.

Initialization is performed using the CON FIG AIN

command. T he syntax is:

CONFIG AIN channel, input, range

Where:

channel is from 0 to 7 for single-ended or

differential. Differential inputs require 2 lines and

are specially paired as shown below. The channels

you specify in a "mixed" application depends upon

what lines ar e used for single ended and differential.

Differential inputs operate in a special way. Use the

following two tables for differ ential inputs.

When channe l = odd

Ch # 0 1 2 3 4 5 6 7

Polarity - + - + - + - +

channel 1 1 3 3 5 5 7 7

J7 pin # 1 3 5 7 9 11 13 15

When channe l = even

Ch # 0 1 2 3 4 5 6 7

Polarity + - + - + - + -

channel 0 0 2 2 4 4 6 6

J7 pin # 1 3 5 7 9 11 13 15

For example, if you wanted one differential input,

channel 0 would use J7 pin nu mber s 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 = ±2.5V and 1 = 0 to

+ 5V.

Differential Mode

When differential m ode is specified, inputs are actually

pseudo-differential. What this means is that a ground

reference is needed. For example, you cannot place a

battery between channel 0 and 1 and get an ac curate

reading. The (-) input must be referenced to ground.

An example of where pseudo-differential works is an

output from a bridge network.

A pseudo-differential input subtracts the DC component

from an input. The IC maker recomm ends the (-) input

remain stable within 1 count with respect to ground for

best results. Connecting a 0.1 uF capacitor from the (-)

input to ground works well.

When operating in differential mode, relative + and -

voltages must be connected to specific inputs. When

inputs are reversed, a conversion returns a 0. When the

relative voltage changes, perform a conversion on the

alternate channel. CONFIG AIN must be perfor med on

both channels to be valid.

Pairs of channels c an be differ ential while others single

ended. Thus, if channel 0 and 1 are differ ential inputs,

channels 2-7 may be single ended.

Examples u sing CON FIG AIN

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, ±2.5V input

CONFIG AIN chan,1,0

1 2 ... 39 40 41 42 43 44 45 46 47 48 49 ... 82 83

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