Philips Semiconductors Product specification
P83C557E4/P80C557E4/P89C557E4Single-chip 8-bit microcontroller
1999 Mar 02
36
6.10 Interrupt System
External events and the real-time-driven on-chip peripherals require
service by the CPU asynchronously to the execution of any
particular section of code. To tie the asynchronous activities of these
functions to normal program execution a multiple-source,
two-priority-level, nested interrupt system is provided. Interrupt
response time in a single-interrupt system is in the range from
2.25µs to 6.75µs when using a 16MHz crystal. The latency time
depends on the sequence of instructions executed directly after an
interrupt request.
The P8xC557E4 acknowledges interrupt requests from 15 sources
as follows (see Figure 34):
• INT0 and INT1 external interrupts
• Timer 0 and Timer 1 internal timer/counter interrupts
• Timer 2 internal timer/counter byte and/or 16-bit overflow, 3
compare and 4 capture interrupts (or 4 additional external
interrupts)
1
• UART serial I/O port receive/transmit interrupt
• I
2
C-bus interface serial I/O interrupt
• ADC autoscan completion interrupt
• ‘Seconds’ timer interrupt SEC (ored with INT1).
For details about seconds timer interrupts, please refer to chapter
6.13.4.
The External Interrupts INT0
and INT1 can each be either
level-activated or transition-activated, depending on bits IT0 and IT1
in register TCON. The flags that actually generate these interrupts
are bits IE0 and IE1 in TCON. When an external interrupt is
generated, the corresponding request flag is cleared by the
hardware when the service routine is vectored to only if the interrupt
was transition-activated. If the interrupt was level-activated then the
interrupt request flag remains set until the external interrupt pin INTx
goes high. Consequently the external source has to hold the request
active until the requested interrupt is actually generated. Then it has
to deactivate the request before the interrupt service routine is
completed, or else another interrupt will be generated. As these
external interrupts are active LOW a “wire-ORing” of several
interrupt sources to one input pin allows expansion.
The Timer 0 and Timer 1 Interrupts are generated by TF0 and TF1,
which are set by a rollover in their respective timer/counter register
(except for Timer 0 in Mode 3 of the serial interface). When a Timer
interrupt is generated, the flag that generated it is cleared by the
on-chip hardware when the service routine is vectored to.
The eight Timer/Counter T2 Interrupt sources are: 4 capture
Interrupts
(1)
, 3 compare interrupts and an overflow interrupt. The
appropriate interrupt request flags must be cleared by software.
The UART Serial Port Interrupt is generated by the logical OR of RI
and TI. Neither of these flags is cleared by hardware. The service
routine will normally have to determine whether it was RI or TI that
generated the interrupt, and the bit will have to be cleared by
software.
The I
2
C Interrupt is generated by bit SI in register S1CON. This flag
has to be cleared by software.
The ADC Interrupt is generated by bit ADINT, which is set when of
all selected analog inputs to be scanned, the conversion is finished.
ADINT must be cleared by software. It cannot be set by software.
The ’Seconds’ timer Interrupt is generated by bit SECINT in register
PLLCON. This flag has to be cleared by software. Note that the
’Seconds’ timer can only be used with the
32 kHz PLL oscillator.
All of the bits that generate interrupts can be set or cleared by
software, with the same result as though it had been set or cleared
by hardware (except the ADC interrupt request flag ADINT, which
cannot be set by software). That is, interrupts can be generated or
pending interrupts can be cancelled in software.
The Interrupts X0, T0, X1, T1, SEC, S0 and S1 are capable to
terminate the Idle Mode.
Interrupt Enable Registers
Each interrupt source can be individually enabled or disabled by
setting or clearing a bit in the interrupt enable special function
registers IEN0 and IEN1. All interrupt sources can also be globally
disabled by clearing bit EA in IEN0. The interrupt enable registers
are described in Figures 34 and 36.
Interrupt Priority Structure
Each interrupt source can be assigned one of two priority levels.
Interrupt priority levels are defined by the interrupt priority special
function registers IP0 and IP1. IP0 and IP1 are described in Figures
37 and 38.
Interrupt priority levels are as follows:
“0”—low priority
“1”—high priority
A low priority interrupt may be interrupted by a high priority interrupt.
A high priority interrupt cannot be interrupted by any other interrupt
source. If two requests of different priority occur simultaneously, the
high priority level request is serviced. If requests of the same priority
are received simultaneously, an internal polling sequence
determines which request is serviced. Thus, within each priority
level, there is a second priority structure determined by the polling
sequence. This second priority structure is shown in Table 37.
Interrupt Handling
The interrupt sources are sampled at S5P2 of every machine cycle.
The samples are polled during the following machine cycle. If one of
the flags was in a set condition at S5P2 of the previous machine
cycle, the polling cycle will find it and the interrupt system will
generate an LCALL to the appropriate service routine, provided this
hardware- generated LCALL is not blocked by any of the following
conditions:
1. An interrupt of higher or equal priority level is already in
progress.
2. The current machine cycle is not the final cycle in the execution
of the instruction in progress. (No interrupt request will be
serviced until the instruction in progress is completed.)
3. The instruction in progress is RETI or any access to the interrupt
priority or interrupt enable registers. (No interrupt will be serviced
after RETI or after a read or write to IP0, IP1, IE0, or IE1 until at
least one other instruction has been subsequently executed.)
NOTE:
1. If a capture register is unused and it’s contents is of no interest, then the corresponding input pin CTnI/P1.n (n: 0...3) may be used as a
(configurable) positive and/or negative edge triggered additional external interrupt input (INT2, INT3, INT4, INT5).
