MC68HC908GP20 Datasheet, PDF (346/406 Pages) Freescale Semiconductor, Inc – M68HC08 Microcontrollers

21.4 Functional Description
NOTE: This module is designed for a 32.768-kHz oscillator.
This module can generate a periodic interrupt by dividing the crystal
frequency, CGMXCLK. The counter is initialized to all 0s when TBON bit
is cleared. The counter, shown in Figure 21-1, starts counting when the
TBON bit is set. When the counter overflows at the tap selected by
TBR2:TBR0, the TBIF bit gets set. If the TBIE bit is set, an interrupt
request is sent to the CPU. The TBIF flag is cleared by writing a 1 to the
TACK bit. The first time the TBIF flag is set after enabling the timebase
module, the interrupt is generated at approximately half of the overflow
period. Subsequent events occur at the exact period.
CGMXCLK
÷2 ÷2 ÷2
÷2
÷2
÷2
÷2
TBON
÷2 ÷2 ÷2 ÷2
÷2 ÷2
÷2 ÷2
000
001
010
011
100
101
110
111
TBMINT
TBIF
TBIE
R
Advance Information
346
Figure 21-1. Timebase Block Diagram
MC68HC908GP20 — Rev 2.1
Freescale Semiconductor