Remote-processing RPC-2350 Manuel d'utilisateur télécharger pdf (Page 60)

CHAPTER 14 MULTI-MODE COUNTER

14-5

inputs to count

130 on tick 0,1 gosub 1000

140 c = 1 :'initialize loop counter

200 bit 0,0,0

210 bit 0,0,1 :'rising edge increments

count

220 a=count(8)

230 if a <> c then print "Count error"

: end

240 inc c

250 goto 200

1000 print count(8) :'show current

count

1010 return

The following example returns a frequency. Input signal

is at J2-9 (A input)

10 OUT &F1,32 :’RESET COUNTER

20 OUT &F1,72 :’ENABLE INPUTS

30 ON TICK 0,1 GOSUB 1000

40 GOTO 40 :’HANG OUT HERE

1000 A = COUNT(8) :’GET COUNT

1010 C = A-B :’FIGURE CHANGE FROM

LAST TIME

1020 PRINT “Frequency = “;a

1030 B = A

1040 RETURN

The first frequency read will be off, due to initialization.

Accuracy is increased by stretching reading to every 10

seconds. Other factors affecting accuracy include serial

communications and other interrupt processing.

The counter will not miss counts. Due to interrupt

latency, some counts will be lar ger than o thers. It is

several counts off at about 8 kHz. If you average the

counts it will be accurate.

Another problem with this routine is periodically, a large

negative number is returned. This is because the counter

has rolled over. This is cor rected by periodically

resetting the CNTR.

Program C NTR2. BAS sets up the LS7166 to cause an

interrupt when a preset number of counts is reached.

W7[2-3] is jumpered to interrupt on a borrow. To

reload the count, bring the LDCTR line (J10-6) low.

When the count is 0 again, another interru pt is

generated. You can also count up provided you bring

counter line ‘B’ (J10-8) low while counter line ‘A’ is

high.

CNTR3.BAS interfaces to a quadrature encoder in x1

mode. The counter is pre-loaded to 100.

NOTE: See CAMBASIC resolution limit below.

CAM BASIC resolution lim it

CAM BASIC stores num bers to 7 digits + exponent.

The counter outputs numbers to 8 digits. This means

that when the counter counts down from 0 to 1677215,

CAM BASIC will store it as 1.67721E+ 7. T he last digit

is dropped.

You can compensate for this easily by introducing an

offset. Preload the counter to some number, say

100,000. This becomes the zero point. W hen the count

is below this number, the counter is in “negative”

territory. See CNTR4.BAS

Program CNTR5.BAS r eads the counter in Basic (not

using CO UN T(8) and prints the value in hex for mat.

This routine can be useful when an external device

triggers the LCTR line (J10-6) to transfer the count to a

latch. The count at that time can be read.

MEASURING PULSE WIDTH

You can measure pulse widths with 217 nano-Second

precision. Widths can be as long as 3.64 Seconds using

the counter input at J10.

There are limitations to measuring pulse widths. Below

lists the major ones.

The pulse repetition r ate must be slower than the time it

takes CAMBASIC to respond to it. As a guide, the

pulse repetition rate should be less than 100 Hz.

Measuring a 50 micro-second signal every second is

easy. Measu ring a 500 micro-second signal every m illi-

second is difficult, if not impossible.

Only logic low pulses are measured. If a high pulse

width is desired, invert the input signal. See figure

below.

1 2 ... 55 56 57 58 59 60 61 62 63 64 65 ... 82 83

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Remote-processing RPC-2350 Manuel d'utilisateur Page 60

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