s908gr16ag4cfj Freescale Semiconductor, Inc, s908gr16ag4cfj Datasheet - Page 211

• Manufacturer Part Number: s908gr16ag4cfj
• Description: M68hc08 Microcontrollers Microcontroller
• Manufacturer: Freescale Semiconductor, Inc

Chapter 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
17.2 Features
Features of the TBM module include:
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
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.
17.4 Interrupts
The timebase module can periodically interrupt the CPU with a rate defined by the selected TBMCLK and
the select bits TBR2–TBR0. When the timebase counter chain rolls over, the TBIF flag is set. If the TBIE
bit is set, enabling the timebase interrupt, the counter chain overflow will generate a CPU interrupt
request.
Freescale Semiconductor
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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
Interrupts must be acknowledged by writing a 1 to the TACK bit.
MC68HC908GR16A Data Sheet, Rev. 1.0
Chapter 5 Configuration Register (CONFIG)
NOTE
Figure
17-1, starts
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