Fixed-Cycle Timer Interrupt Function; Diagram Of Fixed-Cycle Timer Interrupt Function - Epson RA8900SA/CE Applications Manual

RA8900 SA / CE

8.3. Fixed-cycle Timer Interrupt Function

The fixed-cycle timer interrupt generation function generates an interrupt event periodically at any fixed cycle set
between 244.14s and 4095 minutes.
When an interrupt event is generated, the /INT pin goes to low level and "1" is set to the TF bit to report 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 TIE bit is "1". Up to 7.8 ms after the interrupt
occurs, the /INT status is automatically cleared (/INT status changes from low-level to Hi-Z).

Example of
/INT operation
TIE ="1"
TE="0""1"

8.3.1. Diagram of fixed-cycle timer interrupt function

Fixed-cycle timer starts
(1)
TE bit
TIE bit
/INT output
TF bit
Event occurs
(1)
 When the TE bit value changes from "0"to "1" the fixed-cycle timer function starts.
The counter always starts counting down from the preset value when the TE value changes from "0" to "1".
RTC internal operation
Write operation
(1) When a "1" is written to the TE bit, the fixed-cycle timer countdown starts from the preset value.
(2) A fixed-cycle timer interrupt event starts a countdown based on the countdown period (source clock). When the
count value changes from 001h to 000h, an interrupt event occurs.
 After the interrupt event that occurs when the count value changes from 001hto 000h, the counter
automatically reloads the preset value and again starts to count down. (Repeated operation)
(3) When a fixed-cycle timer interrupt event occurs, "1" is written to the TF bit.
(4) When the TF bit = "1" its value is retained until it is cleared to zero.
(5) If the TIE bit = "1" when a fixed-cycle timer interrupt occurs, /INT pin output goes low.
 If the TIE bit = "0" when a fixed-cycle timer interrupt occurs, /INT pin output remains Hi-Z.
(6) Output from the /INT pin remains low during the tRTN period following each event, after which it is automatically
cleared to Hi-Z status.
 /INT is again set low when the next interrupt event occurs.
(7) When a "0" is written to the TE bit, the fixed-cycle timer function is stopped and the /INT pin is set to Hi-Z status.
 When /INT=low, the fixed-cycle timer function is stopped. The tRTN period is the maximum amount of time
before the /INT pin status changes from low to Hi-Z.
(8) As long as /INT=low, the /INT pin status does not change when the TF bit value changes from "1" to "0".
(9) When /INT=low, the /INT pin status changes from low to Hi-Z as soon as the TIE bit value changes from "1" to
"0".
7.8ms
(Max.)
period
Operation of fixed-cycle timer
"1"
(5)
(6)
tRTN
(4)
(3)
period period
(2)
001h000h

Page - 15
TIE="1""0"
(9)
tRTN
tRTN
(8)
 Even when the TF
bit is cleared to zero,
the /INT status does
not change.
period period
Fixed-cycle timer stops
"1"
(7)
"0"
"1"
"0"
Hi-z
(7)
"L"
 Even when the TE bit is
tRTN
cleared to zero, /INT
remains low during the
tRTN time.
"1"
"0"
(7)
ETM44E-01