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CLKSRC12
Internal clock
TM64P_IN12
0
1
Input clock
to timer
Introduction
1470
SPRUH82C – April 2013 – Revised September 2016
Copyright © 2013–2016, Texas Instruments Incorporated
64-Bit Timer Plus
30.1.5.2 Clock Control
The timer can use an internal or external clock source for the counter period. The following sections
explain how to select the clock source.
As shown in
and
, the timer clock source is selected using the clock source
(CLKSRC12) bit in the timer control register (TCR). Two clock sources are available to drive the timer
clock:
•
internal clock by setting CLKSRC12 = 0.
•
external clock on input pin TM64P_IN12 by setting CLKSRC12 = 1.
At reset, the clock source is the internal clock. Details on each of the clock source configuration options
are included in the following sections.
Table 30-1. Timer Clock Source Selection
CLKSRC12
Input Clock
0
Internal clock (default)
1
External clock on timer input
Figure 30-2. Timer Clock Source Block Diagram
30.1.5.2.1 Using the Internal Clock Source to the Timer
The internal clock source to the timer is generated by the PLL controller. This clock source determines the
speed of the timer since the timer counts up in units of source clock cycles. When determining the period
and prescaler settings for the timer, choose the desired period in units of source clock cycles. For details
on the generation of the on-chip clocks, see the
Phase-Locked Loop Controller (PLLC)
chapter.
The CLKSRC12 parameter in the timer control register (TCR) determines whether an internal or external
clock is used as the clock source for the timer. If the timer is configured in 64-bit mode or 32-bit chained
mode, CLKSRC12 controls the clock source for the entire timer. If the timer is configured in dual 32-bit
unchained mode (TIMMODE = 01 in TGCR), CLKSRC12 controls the timer 1:2 side of the timer only.
To select the internal clock as the clock source for the timer, CLKSRC12 in TCR must be cleared to 0.
30.1.5.2.2 Using the External Clock Source to the Timer
An external clock source can be provided to clock the timer through the timer input pin TM64P_IN12. The
CLKSRC12 parameter in the timer control register (TCR) determines whether an internal or external clock
is used as the clock source for the timer. If the timer is configured in 64-bit mode or 32-bit chained mode,
CLKSRC12 controls the clock source for the entire timer. If the timer is configured in dual 32-bit unchained
mode (TIMMODE = 01 in TGCR), CLKSRC12 controls the timer 1:2 side of the timer only.
At reset, the clock source defaults to the internal clock. Details on each of the clock source configuration
options are included in the following sections. To select the external clock as the clock source for the
timer, CLKSRC12 in TCR must be set to 1. The external clock source frequency must be no greater than
the timer peripheral reference clock (see your device-specific data manual).