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2.5
Taking an ITRAP Interrupt
2.6
Internal Pullup Resisters
2.7
PIE Configuration
2.8
Reserved Memory
Taking an ITRAP Interrupt
If an illegal opcode is fetched, the 28x will take an ITRAP (illegal trap) interrupt. During the boot process,
the interrupt vector used by the ITRAP is within the CPU vector table of the boot ROM. As of version 4 of
the boot ROM code, the ITRAP vector points to an interrupt service routine (ISR) within the boot ROM
named ITRAPIsr(). This interrupt service routine attempts to enable the watchdog and then loops forever
until the processor is reset. This ISR will be used for any ITRAP until the user's application initializes and
enables the peripheral interrupt expansion (PIE) block. Once the PIE is enabled, the ITRAP vector located
within the PIE vector table will be used. Prior to boot ROM code version 4, the ITRAP interrupt vector in
the CPU vector table pointed to a RAM location in M0 memory. Refer to
to determine the boot
ROM code version of a particular device.
Each GPIO pin has an internal pullup resistor that can be enabled or disabled in software. The pins that
are read by the boot mode selection code to determine the boot mode selection have pull-ups enabled
after reset by default. In noisy conditions it is still recommended that you configure each of the three boot
mode selection pins externally.
The individual bootloaders SCI, SPI, eCAN, and parallel boot all enable the pullup resistors for the pins
that are used for control and data transfer. The bootloader leaves the resistors enabled for these pins
when it exits. For example, the SCI-A bootloader enables the pullup resistors on the SCITXA and SCIRXA
pins. It is your responsibility to disable them, if desired, after the bootloader exits.
The boot modes do not enable the PIE. It is left in its default state, which is disabled.
The first 80 words of the M1 memory block (address 0x400 - 0x44F) are reserved for the stack and .ebss
code sections during the boot-load process. If code is bootloaded into this region there is no error
checking to prevent it from corrupting the boot ROM stack.
Bootloader Features
20
SPRU722C – November 2004 – Revised October 2006