UPD17P136ACT datasheet(137/292 Pages) NEC

137 / 292 page

CHAPTER 13 PERIPHERAL HARDWARE

118

13.1.6 Setting of Interval Time

The time interval at which the comparator outputs the coincidence signal is determined by the value set to the

modulo register. The set value N of the modulo register is calculated from interval time T [sec] as follows:

T =

N + 1

= (N + 1)

× TCP

fCP

N = T

× fCP – 1 or N =

– 1 (where, N = 1 to 255)

TCP

fCP

: Frequency of count pulse [Hz]

TCP : Cycle of count pulse [sec] (1/fCP = resolution)

• Example of calculating count value from interval time and program

•

Example of setting 7 ms to timer 1 as interval time (system clock: fX = 8 MHz)

Suppose one wanted to set the interval timer to 7 ms. It is impossible to set an interval time of exactly 7 ms

from an 8-MHz system clock. To set an interval time closest to 7 ms, therefore, calculate the count value

by selecting a count pulse (fX/256, resolution: 32

µs) at which the resolution is maximum.

Example of calculation

T = 7 ms, Resolution = 32

µs

– 1

(Resolution)

× 10–3

– 1

× 10–6

= 217.75 = 218 (= DAH)

The value of the modulo register at which the interval time is closest to 7 ms is DAH, and the interval time

at that time is 7.008 ms.

Program example

MOV

DBF0,

#0AH

; Stores DAH to DBF by using reserved words “DBF0” and “DBF1”

MOV

DBF1,

#0DH

; Storage

PUT

TMM,

DBF

; Transfers contents of DBF by using reserved word “TMM”

INITFLG TM1EN, TM1RES, TM1CK1, NOT TM1CK0

; Sets TM1EN and TM1RES, sets count pulse of timer 1 to “fX/256”, and starts

; counting, by using embedded macroinstruction “INITFLG”

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