RX - 8581 SA / JE / NB

8.4. Time Update Interrupt Function

The time update interrupt function generates interrupt events at one-second or one-minute intervals, according to the timing of the internal clock.

When an interrupt event occurs, the UF bit value becomes "1" and the /INT pin goes to low level to indicate that an event has occurred. (However, when a fixed-cycle timer interrupt event has been generated, low-level output from the /INT pin occurs only when the value of the control register's UIE bit is "1". This /INT status is automatically cleared (/INT status changes from low level to Hi-Z) 7.8 ms (fixed value) after the interrupt occurs.

∗ /INT operation example

7.8ms

UIE = " 1 "

period

UIE = " 1 " → " 0 "

8.4.1. Time update interrupt function diagram

" 1 "(7)

UIE bit

(4)

 

/INT output

(5)

 

tRTN

UF bit

(3)

(2)

period

period

 

 

 

 

 

 

 

 

 

 

 

" 1 "

 

 

 

 

 

 

 

 

 

 

" 0 "

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Hi - z

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

" L "

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

tRTN

 

 

 

 

tRTN

tRTN

 

(6)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

∗

/INT status does not

 

 

 

 

 

 

 

 

 

 

 

" 1 "

 

 

change when UF bit is

 

 

 

 

 

 

 

 

 

cleared to zero.

 

 

 

 

" 0 "

 

 

 

 

 

 

 

 

 

 

period period

Events

(1)

 

Operation in RTC

Write operation

(1)A time update interrupt event occurs when the internal clock's value matches either the second update time or the minute update time. The USEL bit's specification determines whether it is the second update time or the minute update time that must be matched.

(2)When a time update interrupt event occurs, the UF bit value becomes "1".

(3)When the UF bit value is "1" its value is retained until it is cleared to zero.

(4)When a time update interrupt occurs, /INT pin output is low if UIE = "1".

∗If UIE = "0" when a timer update interrupt occurs, the /INT pin status remains Hi-Z.

(5)Each time an event occurs, /INT pin output is low only up to the tRTN time (which is fixed as 7.1825 ms for time update interrupts) after which it is automatically cleared to Hi-Z.

∗/INT pin output goes low again when the next interrupt event occurs.

(6)As long as /INT = low, the /INT pin status does not change, even if the UF bit value changes from "1" to "0".

(7)When /INT = low, the /INT pin status changes from low to Hi-Z as soon as the UIE bit value changes from "1" to "0".

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MQ372-02