MC81F4x16
11.3 BRK Interrupt
Software interrupt can be invoked by BRK instruction, which has the lowest priority order. Interrupt
vector address of BRK is shared with the vector of TCALL 0 (Refer to Program Memory Section).
When BRK interrupt is generated, B-flag of PSW is set to distinguish BRK from TCALL 0.
Each processing step is determined by B-flag as shown in Figure
11.4 Shared Interrupt Vector
Some interrupts share the interrupt vector address. To recognize which interrupt is occurred, some
interrupt flag registers are used.
Note that, interrupt request bits are cleared after call the interrupt service routine. So interrupt request
bits can not be used to recognize which interrupt is occurred.
UART
In case of using interrupts of UART Tx and UART Rx together, it is necessary to check UTIF and
URIF in the interrupt service routine to find out which interrupt is occurred. Because the UART Tx and
UART Rx share the one interrupt vector address. These flag bits must be cleared by software after
reading this register. ( UTIF and URIF are placed in INTFL register )
External Interrupt Group
In case of using interrupts of Ext group. It is necessary to check the EINTF register in the interrupt
service routine to find out which external interrupt is occurred. Because the 8 external interrupts share
the one interrupt vector address. These flag bits must be cleared by software after reading this
register.
Timer match / overflow
In case of using interrupts of Timer match and overflow together, it is necessary to check the INTFH
register in the interrupt service routine to find out which interrupt is occurred. Because the timer match
and overflow share the on interrupt vector address. See „INTFH‟ on page 91 to know which bit is
which.
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October 19, 2009 Ver.1.35
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