Clock Circuitry; Watchdog Timer; Exception Sources - Motorola M5271EVB User Manual

1.3.2

Clock Circuitry

The are three options to provide the clock to the CPU. These options can be configured by
setting JP[10:12]. See Table 1-11., "M5271EVB Clock Source Selection"
Table 1-11. M5271EVB Clock Source Selection
JP10 JP11
1-2 1-2
2-3 1-2
X 2-3
The 25MHz oscillator (U15) also feeds the Ethernet chip (U9).
1.3.3

Watchdog Timer

The dBUG Firmware does NOT enable the watchdog timer on the MCF5271.
1.3.4

Exception Sources

The ColdFire® family of processors can receive seven levels of interrupt priorities. When
the processor receives an interrupt which has a higher priority than the current interrupt
mask (in the status register), it will perform an interrupt acknowledge cycle at the end of
the current instruction cycle. This interrupt acknowledge cycle indicates to the source of the
interrupt that the request is being acknowledged and the device should provide the proper
vector number to indicate where the service routine for this interrupt level is located. If the
source of interrupt is not capable of providing a vector, its interrupt should be set up as an
autovector interrupt which directs the processor to a predefined entry in the exception table
(refer to the MCF5271 User's Manual).
The processor goes to an exception routine via the exception table. This table is stored in
the Flash EEPROM. The address of the table location is stored in the VBR. The dBUG
ROM monitor writes a copy of the exception table into the RAM starting at $00000000. To
set an exception vector, the user places the address of the exception handler in the
appropriate vector in the vector table located at $00000000 and then points the VBR to
$00000000.
The MCF5271 microprocessor has seven external interrupt request lines IRQ[7:1]. The
interrupt controller is capable of providing up to 63 interrupt sources. These sources are:-
• External interrupt signals IRQ[7:1] (EPORT)
• Software watchdog timer module
• Timer modules
• UART modules 0, 1 and 2
2
• I C module
JP12 Clock Selection
ON 25MHz Oscillator (default setting)
ON 25MHz External Clock
OFF 25MHz Crystal (not populated)
Chapter 1. M5271EVB Introduction
Support Logic
1-11