MC9S12T64 Datasheet, PDF(31/608 Page) Motorola, Inc – Specification

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MC9S12T64 Datasheet, PDF (31/608 Pages) Motorola, Inc – Specification

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Freescale Semiconductor, Inc.

Central Processing Unit (CPU)

Programming Model

(MCUs). Nonmaskable interrupts are typically used to deal with major

system failures such as loss of power. However, enabling

nonmaskable interrupts before a system is fully powered and

initialized can lead to spurious interrupts. The X bit provides a

mechanism for masking nonmaskable interrupts until the system is

stable.

Reset sets the X bit. As long as the X bit remains set, interrupt service

requests made via the XIRQ pin are not recognized. Software must

clear the X bit to enable interrupt service requests from the XIRQ pin.

Once software clears the X bit, enabling XIRQ interrupt requests, only

a reset can set it again. The X bit does not affect I bit maskable

interrupt requests.

When the X bit is clear and an XIRQ interrupt request occurs, the CPU

stacks the cleared X bit. It then automatically sets the X and I bits in

the CCR to disable XIRQ and maskable interrupt requests during the

XIRQ interrupt service routine.

An RTI instruction at the end of the interrupt service routine restores

the cleared X bit to the CCR, re-enabling XIRQ interrupt requests.

1 = XIRQ interrupt requests disabled

0 = XIRQ interrupt requests enabled

H â Half-Carry Bit

The H bit indicates a carry from bit 3 of the result during an addition

operation. The DAA instruction uses the value of the H bit to adjust

the result in accumulator A to BCD format. ABA, ADD, and ADC are

the only instructions that update the H bit.

1 = Carry from bit 3 after ABA, ADD, or ADC instruction

0 = No carry from bit 3 after ABA, ADD, or ADC instruction

I â Interrupt Mask Bit

Clearing the I bit enables maskable interrupt sources. Reset sets the

I bit. To enable maskable interrupt requests, software must clear the

I bit. Maskable interrupt requests that occur while the I bit is set

remain pending until the I bit is cleared.

Central Processing Unit (CPU)

For More Information On This Product,

Go to: www.freescale.com

MC9S12T64Revision 1.1.1

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