参数资料
型号: TMS320C2812ZHHS
厂商: TEXAS INSTRUMENTS INC
元件分类: 数字信号处理
英文描述: 16-BIT, 150 MHz, OTHER DSP, PBGA179
封装: LEAD FREE, BGA-179
文件页数: 106/156页
文件大小: 1826K
代理商: TMS320C2812ZHHS
Functional Overview
53
April 2001 Revised October 2005
SPRS174M
3.8.1
Loss of Input Clock
In PLL enabled mode, if the input clock XCLKIN or the oscillator clock is removed or absent, the PLL will still
issue a “limp-mode” clock. The limp-mode clock will continue to clock the CPU and peripherals at a typical
frequency of 14 MHz. The PLLCR register should have been written to with a non-zero value for this feature
to work.
Normally, when the input clocks are present, the watchdog counter will decrement to initiate a watchdog reset
or WDINT interrupt. However, when the external input clock fails, the watchdog counter will stop decrementing
(i.e., the watchdog counter does not change with the limp-mode clock). This condition could be used by the
application firmware to detect the input clock failure and initiate necessary shut-down procedure for the
system.
NOTE:
Applications in which the correct CPU operating frequency is absolutely critical must
implement a mechanism by which the DSP will be held in reset, should the input clocks ever
fail. For example, an R-C circuit may be used to trigger the XRS pin of the DSP, should the
capacitor ever get fully charged. An I/O pin may be used to discharge the capacitor on a
periodic basis to prevent it from getting fully charged. Such a circuit would also help in
detecting failure of the VDD3VFL rail.
3.9
PLL-Based Clock Module
The F281x and C281x have an on-chip, PLL-based clock module. This module provides all the necessary
clocking signals for the device, as well as control for low-power mode entry. The PLL has a 4-bit ratio control
to select different CPU clock rates. The watchdog module should be disabled before writing to the PLLCR
register. It can be re-enabled (if need be) after the PLL module has stabilized, which takes 131 072 XCLKIN
cycles.
The PLL-based clock module provides two modes of operation:
Crystal-operation
This mode allows the use of an external crystal/resonator to provide the time base to the device.
External clock source operation
This mode allows the internal oscillator to be bypassed. The device clocks are generated from an external
clock source input on the X1/XCLKIN pin.
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