Remote-processing RPC-220 Manual de usuario descargar pdf (Pagina 39)

PWM AND ANALOG OUTPUT SECTION 12

PAGE 12-2

Second is step response time. Pulses are filtered through

a 1 pole filter. This means there is some delay time

from when the duty cycle changes to output change.

Generally, this is about 100 ms for small steps and 200

ms for larger (1/2 scale) steps.

Analog outputs are at J1. J1-17 is analog output 0 while

J1-19 is analog output 1. Output channels are controlled

by their corresponding P WM channel.

Example program PWM.C under directory PWM

generates a ram p on the analog outputs by continuously

varying the duty cycle.

Measuring outputs using on card A-D

The analog outputs can be set to a more precise level by

reading them at the A-D input. D ue to interactions

between the analog output and A-D circuits, a 20K ohm

or greater resistor should be placed between A-D input

and output. If the resistor is not installed, A-D

conversions intermittently read full scale (1023 counts).

Output leve ls and noise

The operational am plifier used to buffer outputs gets its

power from the RS-232 generator. If you turn of the

RS-232 output, its quite probable analog output will be

affected.

There is some noise (ripple) on the analog outputs. This

noise comes from two sources: First is the PWM signal

it self. If the CPU PWMP register is programmed for a

low frequency, there will be ripple on the output. To

correct this problem, decrea se the value w ritten to

PWMP to 0x10 or lower.

The second noise source is the RS-232 generator. The

RS-232 chip U9 generates both + and - voltages in the 8

volt range. The positive voltage is somewhat filtered.

The negative is not. To clean up the negative voltage,

put a 10 micro-farad or larger capacitor on the -V pin at

J1-20. Capacitor voltage should be 16 volts or higher.

PIN OUTS AND REGISTER

INFORMATION

The following tables are partial pin outs for J1 and J3.

Full pin out for J1 is in SECTION 11 and J3 in

SECTION 6.

Pin outs

Conn Function

J1-17 Analog output, c hannel 0

J1-19 Analog output, channel 1

J3-22 PWM output, channel 0

J3-20 PWM output, channel 1

PWM registers

(in special

function area)

PWMP 0xfe Prescaler

PWM 0 0xfc Duty cycle

PWM 1 0xfd Duty cycle

APPLICATION PROGRAM

The following program is in the PWM directory. A

brief description follows:

File name Description

PWM.C Initializes PWM prescaler and varies

duty cycle from 0 to 100%. U sed also

to view voltage ramp from analog

outputs.

1 2 ... 34 35 36 37 38 39 40 41 42 43 44 45 46 47

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Remote-processing RPC-220 Manual de usuario Pagina 39

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