C8051F350-TB Silicon Laboratories Inc, C8051F350-TB Datasheet - Page 105
C8051F350-TB
Manufacturer Part Number
C8051F350-TB
Description
PROTOTYPINGBOARDWITH C8051F350
Manufacturer
Silicon Laboratories Inc
Type
MCUr
Specifications of C8051F350-TB
Contents
Board
Processor To Be Evaluated
C8051F35x
Interface Type
USB
Silicon Manufacturer
Silicon Labs
Core Architecture
8051
Silicon Core Number
C8051F350
Silicon Family Name
C8051F35x
Kit Contents
Board
Lead Free Status / RoHS Status
Contains lead / RoHS non-compliant
For Use With/related Products
C8051F350
Lead Free Status / Rohs Status
Lead free / RoHS Compliant
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C8051F350/1/2/3
12. Interrupt Handler
The C8051F35x family includes an extended interrupt system supporting a total of 12 interrupt sources
with two priority levels. The allocation of interrupt sources between on-chip peripherals and external input
pins varies according to the specific version of the device. Each interrupt source has one or more associ-
ated interrupt-pending flag(s) located in an SFR. When a peripheral or external source meets a valid inter-
rupt condition, the associated interrupt-pending flag is set to logic 1.
If interrupts are enabled for the source, an interrupt request is generated when the interrupt-pending flag is
set. As soon as execution of the current instruction is complete, the CPU generates an LCALL to a prede-
termined address to begin execution of an interrupt service routine (ISR). Each ISR must end with an RETI
instruction, which returns program execution to the next instruction that would have been executed if the
interrupt request had not occurred. If interrupts are not enabled, the interrupt-pending flag is ignored by the
hardware and program execution continues as normal. (The interrupt-pending flag is set to logic 1 regard-
less of the interrupt's enable/disable state.)
Each interrupt source can be individually enabled or disabled through the use of an associated interrupt
enable bit in the Interrupt Enable and Extended Interrupt Enable SFRs. However, interrupts must first be
globally enabled by setting the EA bit (IE.7) to logic 1 before the individual interrupt enables are recog-
nized. Setting the EA bit to logic 0 disables all interrupt sources regardless of the individual interrupt-
enable settings. Note that interrupts which occur when the EA bit is set to logic 0 will be held in a pending
state, and will not be serviced until the EA bit is set back to logic 1.
Some interrupt-pending flags are automatically cleared by the hardware when the CPU vectors to the ISR.
However, most are not cleared by the hardware and must be cleared by software before returning from the
ISR. If an interrupt-pending flag remains set after the CPU completes the return-from-interrupt (RETI)
instruction, a new interrupt request will be generated immediately and the CPU will re-enter the ISR after
the completion of the next instruction.
12.1. MCU Interrupt Sources and Vectors
The MCUs support 12 interrupt sources. Software can simulate an interrupt by setting any interrupt-pend-
ing flag to logic 1. If interrupts are enabled for the flag, an interrupt request will be generated and the CPU
will vector to the ISR address associated with the interrupt-pending flag. MCU interrupt sources, associ-
ated vector addresses, priority order and control bits are summarized in Table 12.1 on page 106. Refer to
the datasheet section associated with a particular on-chip peripheral for information regarding valid inter-
rupt conditions for the peripheral and the behavior of its interrupt-pending flag(s).
12.2. Interrupt Priorities
Each interrupt source can be individually programmed to one of two priority levels: low or high. A low prior-
ity interrupt service routine can be preempted by a high priority interrupt. A high priority interrupt cannot be
preempted. Each interrupt has an associated interrupt priority bit in an SFR (IP or EIP1) used to configure
its priority level. Low priority is the default. If two interrupts are recognized simultaneously, the interrupt with
the higher priority is serviced first. If both interrupts have the same priority level, a fixed priority order is
used to arbitrate, given in Table 12.1.
12.3. Interrupt Latency
Interrupt response time depends on the state of the CPU when the interrupt occurs. Pending interrupts are
sampled and priority decoded each system clock cycle. Therefore, the fastest possible response time is 5
system clock cycles: 1 clock cycle to detect the interrupt and 4 clock cycles to complete the LCALL to the
ISR. If an interrupt is pending when a RETI is executed, a single instruction is executed before an LCALL
Rev. 1.1
105
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