MC68HC05E0 Datasheet, PDF (65/96 Pages) Motorola, Inc – High-density complementary metal oxide semiconductor (HCMOS) microcontroller unit

7.5
Real Time Interrupt Timer
The Real Time Interrupt circuit consists of a three stage divider and a 1 of 4 selector. The clock signal
which drives the RTI circuit is P02/2¹⁴ (= P02/16384) with three additional divider stages giving a
maximum interrupt period of 32.8 milliseconds at a bus frequency of 4 MHz (See Figure 4-1).
The 8-bit RTI Timer Counter Register ($0019) is a read only register which contains the current
value of the 8-bit ripple counter at the beginning of the timer chain. Reset clears the counter.
During WAIT mode the CPU clock halts but the timer remains active. If the RTIE bit is set, a timer
interrupt will cause the processor to exit the WAIT mode. The timer is cleared when entering STOP
mode.
RTI Counter
Register ($0019)
Divide
8-bit Freerunning
Bus Frequency P02
by 4
Counter
8
7
7-bit
Counter
RTI Select
Data
Bus
RTI Control Register ($0018)
RTIF
RTIE
RT1 RT0
8
IRQB
MC68HC05E0
Figure 7-4 Real Time Interrupt Timer Structure
TIMERS
MOTOROLA
7-5