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3.2.10
Peripheral Interrupt Expansion (PIE) Block
3.2.11
External Interrupts (XINT1, XINT2, XNMI)
3.2.12
Oscillator and PLL
3.2.13
Watchdog
3.2.14
Peripheral Clocking
3.2.15
Low-Power Modes
TMS320F28044
Digital Signal Processor
SPRS357B–AUGUST 2006–REVISED MAY 2007
The PIE block serves to multiplex numerous interrupt sources into a smaller set of interrupt inputs. The
PIE block can support up to 96 peripheral interrupts. On the F28044 device, 43 of the possible 96
interrupts are used by peripherals. The 96 interrupts are grouped into blocks of 8 and each group is fed
into 1 of 12 CPU interrupt lines (INT1 to INT12). Each of the 96 interrupts is supported by its own vector
stored in a dedicated RAM block that can be overwritten by the user. The vector is automatically fetched
by the CPU on servicing the interrupt. It takes 8 CPU clock cycles to fetch the vector and save critical
CPU registers. Hence the CPU can quickly respond to interrupt events. Prioritization of interrupts is
controlled in hardware and software. Each individual interrupt can be enabled/disabled within the PIE
block.
The F28044 device supports three masked external interrupts (XINT1, XINT2, XNMI). XNMI can be
connected to the INT13 or NMI interrupt of the CPU. Each of the interrupts can be selected for negative,
positive, or both negative and positive edge triggering and can also be enabled/disabled (including the
XNMI). The masked interrupts also contain a 16-bit free running up counter, which is reset to zero when a
valid interrupt edge is detected. This counter can be used to accurately time stamp the interrupt. Unlike
the 281x devices, there are no dedicated pins for the external interrupts. Rather, any Port A GPIO pin can
be configured to trigger any external interrupt.
The F28044 device can be clocked by an external oscillator or by a crystal attached to the on-chip
oscillator circuit. A PLL is provided supporting up to 10 input-clock-scaling ratios. The PLL ratios can be
changed on-the-fly in software, enabling the user to scale back on operating frequency if lower power
operation is desired. Refer to the Electrical Specification section for timing details. The PLL block can be
set in bypass mode.
The F28044 device contains a watchdog timer. The user software must regularly reset the watchdog
counter within a certain time frame; otherwise, the watchdog will generate a reset to the processor. The
watchdog can be disabled if necessary.
The clocks to each individual peripheral can be enabled/disabled so as to reduce power consumption
when a peripheral is not in use. Additionally, the system clock to the serial ports (except I
2
C) and the ADC
blocks can be scaled relative to the CPU clock. This enables the timing of peripherals to be decoupled
from increasing CPU clock speeds.
The F28044 device is full static CMOS devices. Three low-power modes are provided:
IDLE:
Place CPU into low-power mode. Peripheral clocks may be turned off selectively and only
those peripherals that need to function during IDLE are left operating. An enabled interrupt
from an active peripheral or the watchdog timer will wake the processor from IDLE mode.
Turns off clock to CPU and peripherals. This mode leaves the oscillator and PLL functional.
An external interrupt event will wake the processor and the peripherals. Execution begins
on the next valid cycle after detection of the interrupt event
Turns off the internal oscillator. This mode basically shuts down the device and places it in
the lowest possible power consumption mode. A reset or external signal can wake the
device from this mode.
STANDBY:
HALT:
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Functional Overview
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