FS98O24 datasheet(37/77 Pages) FORTUNE

37 / 77 page

input CPI. The counters will not stop counting until CTA overflows and after the first positive edge signal

from input CPI, and then the system will send out an interrupt signal. Therefore, we can count the cycles

of CPI input signal to calculate the high-resolution frequency and duty cycle of the low frequency input

signal by the following calculation approach.



Under mode FCM=10, CTA and CTB start counting when FCRST=1. The counters will not stop counting

until CTA overflows, and then the system will send out an interrupt signal. The calculating flows and

methods are described as follows:

Frequency Measurement Mode: FCM=00=11

(1)

Load=1, FCRST=0.

(2)

Write to CTA [23:8] to set initial value of CTAI.

(3)

Set GT [2:0] to select the length of counter CTA. GT=000 sets CTA [23:8] as a 16-bit counter and

CTA [7] is as the clock input; CTA [23:0] is a 24-bit counter. GT=111 sets CTA [23:8] as a 16-bit

counter and CTA [0] is as the clock input; {CTA [23:8], CTA [0]} is set as a 17-bit counter.

(4)

Gate Time = (1000000h-CTAI x 256) x 1us … if GT=000.

(5)

Set LOAD=0, FCRST=1, and CPI frequency starts measuring.

(6)

Wait till positive edge of CPI, then Start=1 and CTA and CTB start counting.

(7)

Wait till CTA overflows and at the next positive edge of CPI, then Start=0 and CTA and CTB stop

counting.

(8)

When the CPU receives interrupt signal, the CPU will read CTA and CTB. Here CTA is the reference

clock counter, and CTB is the input clock counter.

(9)

Frequency of CPI is

















CTA

CTAI

CTB

DCK

. Go to (1) for next measurement.

Duty Cycle Measurement Mode: FCM=01

(1)

Load=1, FCRST=0.

(2)

Write to CTA [23:8] to set initial value of CTAI.

(3)

Set GT [2:0] to select the length of counter CTA. GT=000 sets CTA [23:8] as a 16-bit counter and

CTA [7] is as the clock input; CTA [23:0] is a 24-bit counter. GT=111 sets CTA [23:8] as a 16-bit

counter and CTA [0] is as the clock input; {CTA [23:8], CTA [0]} is set as a 17-bit counter.

(4)

Gate Time = (1000000h-CTAI x 256) x 1us … if GT=000.

(5)

Set LOAD=0, FCRST=1, and CPI frequency starts measuring.

(6)

Wait till positive edge of CPI, then Start=1 and CTA and CTB start counting.

(7)

Wait till CTA overflows and at the next positive edge of CPI, then Start=0 and CTA and CTB stop

counting.

(8)

When the CPU receives interrupt signal, the CPU will read CTA and CTB. Here CTA is the reference

clock counter, and CTB is the input clock high pulse width counter.

(9)

The duty cycle of CPI is

















CTA

CTAI

CTB

100

. Go to (1) for next measurement.

Timer Mode: FCM=10

(1)

Load=1, FCRST=0.

(2)

Write to CTA [23:8] to set initial value of CTAI.

(3)

Set GT [2:0] to select the length of counter CTA. GT=000 sets CTA [23:8] as a 16-bit counter and

CTA [7] is as the clock input; CTA [23:0] is a 24-bit counter. GT=111 sets CTA [23:8] as a 16-bit

counter and CTA [0] is as the clock input; {CTA [23:8], CTA [0]} is set as a 17-bit counter.

(4)

Gate Time = (1000000h-CTAI x 256) x 1us … if GT=000.

(5)

When CTA overflows, then send interrupt signal to the CPU.

(6)

If CPU receives interrupt signal, then Go to (1).

CNS: Frequency Counter Input Select

(1)

If CNS=1, Frequency Counter Input=CPOUT. If CNS=0, Frequency Counter Input=CNTI.

FS98O24 Datasheet(PDF) 37 Page - Fortune Semiconductor Corp.

FS98O24 Datasheet(HTML) 37 Page - Fortune Semiconductor Corp.

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77

Datasheet Download

Link URL