UPD17708 datasheet(272/356 Pages) NEC

272 / 356 page

272

µPD17704, 17705, 17707, 17708, 17709

18. FREQUENCY COUNTER

18.1 Outline of Frequency Counter

Figure 18-1 outlines the frequency counter.

The frequency counter has an IF counter function to count the intermediate frequency (IF) of an external input signal

and an external gate counter (FCG: Frequency Counter for external Gate signal) to detect the pulse width of an external

input signal.

The IF counter function counts the frequency input to the P1C0/FMIFC or P1C1/AMIFC pin at fixed intervals (1

ms, 4 ms, 8 ms, or open) by using a 16-bit counter.

The external gate counter function counts the frequency of the internal clock (1 kHz, 100 kHz, 900 kHz) from the

rising to the falling of the signal input to the P2A1/FCG1 or P2A0/FCG0 pin.

The IF counter and external gate counter functions cannot be used at the same time.

Figure 18-1. Outline of Frequency Counter

I/O selection

block

Gate time

control block

Start/stop control

block

IF counter

(16 bits)

P2A1/FCG1

FCGCH1 flag

FCGCH0 flag

IFCCK1 flag

IFCCK0 falg

IFCSTRT flag

DBF

IFCGOSTT flag

IFCRES flag

IFCMD1 flag

IFCMD0 flag

P2A0/FCG0

P1C0/FMIFC

P1C1/AMIFC

Remarks 1.

FCGCH1 and FCGCH0 (bits 1 and 0 of FCG channel selection register: refer to Figure 18-4) select

the pin used for the external gate counter function.

IFCMD1 and IFCMD0 (bits 3 and 2 of IF counter mode selection register: refer to Figure 18-3) select

the IF counter or external gate counter function.

IFCCK1 and IFCCK0 (bits 1 and 0 of IF counter mode selection register: refer to Figure 18-3) select

the gate time of the IF counter function and the reference frequency of the external gate counter

function.

IFCSTRT (bit 1 of IF counter control register: refer to Figure 18-6) control starting of the IF counter

and external gate counter functions.

IFCGOSTT (bit 0 of IF counter gate status detection register: refer to Figure 18-7) detects opening/

closing the gate of the IF counter function.

IFCRES (bit 0 of IF counter control register: refer to Figure 18-6) reset the count value of the IF

counter.

UPD17708 Datasheet(PDF) 272 Page - NEC

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