MC68HC908GR16 Datasheet, PDF (239/310 Pages) Motorola, Inc – Microcontrollers

Freescale Semiconductor, Inc.
Data Sheet — MC68HC908GR16
Section 17. Timebase Module (TBM)
17.1 Introduction
This section describes the timebase module (TBM). The TBM will generate
periodic interrupts at user selectable rates using a counter clocked by the external
clock source. This TBM version uses 15 divider stages, eight of which are user
selectable. A configuration option bit to select an additional 128 divide of the
external clock source can be selected. See Section 5. Configuration Register
(CONFIG)
17.2 Features
Features of the TBM module include:
• External clock or an additional divide-by-128 selected by configuration
option bit as clock source
• Software configurable periodic interrupts with divide-by: 8, 16, 32, 64, 128,
2048, 8192, and 32768 taps of the selected clock source
• Configurable for operation during stop mode to allow periodic wakeup from
stop
17.3 Functional Description
This module can generate a periodic interrupt by dividing the clock source supplied
from the clock generator module, CGMXCLK.
The counter is initialized to all 0s when TBON bit is cleared. The counter, shown in
Figure 17-1, 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.
The timebase module may remain active after execution of the STOP instruction if
the crystal oscillator has been enabled to operate during stop mode through the
OSCENINSTOP bit in the configuration register. The timebase module can be
used in this mode to generate a periodic wakeup from stop mode.
MC68HC908GR16 — Rev. 1.0
MOTOROLA
Timebase Module (TBM)
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Data Sheet
239