mc68hc711d3 Freescale Semiconductor, Inc, mc68hc711d3 Datasheet - Page 52

• Manufacturer Part Number: mc68hc711d3
• Description: M Hc11 Microcontrollers Microcontroller
• Manufacturer: Freescale Semiconductor, Inc

Resets, Interrupts, and Low-Power Modes
When an I bit related interrupt occurs, the I bit is automatically set by hardware after stacking the CCR
byte. The X bit is not affected. When an X bit related interrupt occurs, both the X and the I bit are
automatically set by hardware after stacking the CCR. A return-from-interrupt (RTI) instruction restores
the X and I bits to their preinterrupt request state.
4.3.5 Priority Structure
Interrupts obey a fixed hardware priority circuit to resolve simultaneous requests. However one I bit
related interrupt source may be elevated to the highest I bit priority in the resolution circuit.
Six interrupt sources are not masked by the I bit in the CCR and have these fixed priority relationships:
SWI is actually an instruction and has highest priority, other than resets, in that once the SWI opcode is
fetched, no other interrupt can be honored until the SWI vector has been fetched.
Each of the previous sources is an input to the priority resolution circuit. The highest I bit masked priority
input to the resolution circuit is assigned to be connected to any one of the remaining I bit related interrupt
sources. This assignment is made under the software control of the HPRIO register. To avoid timing
races, the HPRIO register can be written only while the I bit related interrupts are inhibited (I bit of CCR
is logic 1). An interrupt that is assigned to this higher priority position is still subject to masking by any
associated control bits or by the I bit in the CCR. The interrupt vector address is not affected by assigning
a source to the higher priority position.
Figure
Figure 4-4
fetches.
Figure 4-6
sources within the SCI subsystem.
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1. Reset
2. Clock monitor failure
3. COP failure
4. Illegal opcode
5. SWI
6. XIRQ
4-4,
Figure 4-5
shows how the CPU begins from a reset, and how interrupt detection relates to normal opcode
is an expansion of the SCI interrupt block of
Figure
4-5, and
is an expansion of a block in
Figure 4-6
MC68HC711D3 Data Sheet, Rev. 2.1
illustrate the interrupt process as it relates to normal processing.
Figure 4-4
Figure 4-4
and shows how interrupt priority is resolved.
and shows the resolution of interrupt
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