mc68hc705j2 Freescale Semiconductor, Inc, mc68hc705j2 Datasheet - Page 61

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mc68hc705j2

Manufacturer Part Number
mc68hc705j2
Description
8-bit Microcontroller
Manufacturer
Freescale Semiconductor, Inc
Datasheet
TOF — Timer Overflow Flag
RTIF — Real-Time Interrupt Flag
TOIE — Timer Overflow Interrupt Enable
RTIE — Real-Time Interrupt Enable
Bits 3 and 2 — Not used. Always read as zeros.
RT1, RT0 — Real-Time 1 and 0
MC68HC705J2
RT1:RT0
This clearable, read-only bit becomes set when the first eight stages of the counter
roll over from $FF to $00. TOF generates a timer overflow interrupt request if TOFE
is also set. Clear TOF by writing a zero to it. Writing a one to TOF has no effect.
This clearable, read-only bit becomes set when the selected RTI output becomes
active. RTIF generates a real-time interrupt request if RTIE is also set. Clear RTIF
by writing a zero to it. Writing a one to RTIF has no effect.
This read/write bit enables timer overflow interrupts.
This read/write bit enables real-time interrupts
These read/write bits select one of four real-time interrupt rates. See Table 7-1.
The real-time interrupt rate should be selected by reset initialization software. A
reset sets both RT1 and RT0, selecting the lowest real-time interrupt rate.
Changing the real-time interrupt rate near the end of the RTI period or during a
cycle in which the counter is switching can produce unpredictable results.
Because the selected RTI output drives the COP timer, changing the real-time
interrupt rate also changes the counting rate of the COP timer.
0 0
0 1
1 0
1 1
1 = Timer overflow interrupts enabled
0 = Timer overflow interrupts disabled
1 = Real-time interrupts enabled
0 = Real-time interrupts disabled
RTI
f op 2
f op 2
f op 2
f op 2
Table 7-1. Real-Time Interrupt Rate Selection
Rate
14
15
16
17
(f o p = 2 MHz)
RTI Period
16.4 ms
32.8 ms
65.5 ms
8.2 ms
TIMER
COP Timeout Period
(-0/+1 RTI Period)
7 RTI Period
7 RTI Period
7 RTI Period
7 RTI Period
Minimum COP Timeout
Period ( f o p = 2 MHz)
114.7 ms
229.4 ms
458.8 ms
57.3 ms
MOTOROLA
7-3

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