参数资料
型号: P83C180
厂商: NXP SEMICONDUCTORS
元件分类: 微控制器/微处理器
英文描述: Microcontrollers for monitors with DDC interface, auto-sync detection and sync proc(带DDC接口,同步监测和同步处理的监视器微控制器)
中文描述: 8-BIT, MROM, 16 MHz, MICROCONTROLLER, PDIP42
封装: 0.600 INCH, PLASTIC, SOT-270-1, SDIP-42
文件页数: 19/84页
文件大小: 420K
代理商: P83C180
1997 Dec 12
19
Philips Semiconductors
Product specification
Microcontrollers for monitors with DDC
interface, auto-sync detection and sync proc.
P83Cx80; P87C380
8.2
How interrupts are handled
The interrupt flags are sampled at the S5P2 state 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 preceding 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 equal priority or higher priority level is
already in progress.
2.
The current (polling) cycle is not the final cycle in the
execution of the instruction in progress.
3.
The instruction in progress is RETI or any write to the
IE or IP registers.
Any of these conditions will block the generation of the
LCALL to the interrupt service routine. Condition 2
ensures that the instruction in progress will be completed
before vectoring to any service routine.
Condition 3 ensures that if the instruction in progress is
RETI or any access to IE or IP, then at least one more
instruction will be executed before the interrupt is vectored
to.The polling cycle is repeated with each machine cycle,
and the values polled are the values that were present at
S5P2 of the previous machine cycle. Note that if an
interrupt flag is active but not being responded to for one
of the above mentioned conditions, and if the flag is still
inactive when the blocking condition is removed, then the
denied interrupt will not be serviced. In other words, the
fact that the interrupt flag was once active but not serviced
is not remembered. Every polling cycle is new.
The polling cycle/LCALL sequence is illustrated in “Data
Handbook IC20; 80C51 family hardware description;
Figure: Interrupt Response Timing Diagram”
Note that if an interrupt of higher priority level becomes
active prior to S5P2 of the machine cycle labelled C3 (see
“Data Handbook IC20; 80C51 family hardware description;
Figure: Interrupt Response Timing Diagram”), then in
accordance with the above rules it will be vectored to
during C5 and C6, without any instruction of the lower
priority routine having been executed. Thus the processor
acknowledges an interrupt request by executing a
hardware generated LCALL to the appropriate servicing
routine. The hardware generated LCALL pushes the
contents of the Program Counter on to the stack (but it
does not save the PSW) and reloads the PC with an
address that depends on the source of the interrupt being
vectored to as shown in Table 22.
Execution proceeds from that location until the RETI
instruction is encountered. The RETI instruction informs
the processor that the interrupt routine is no longer in
progress, then pops the top two bytes from the stack and
reloads the Program Counter. Execution of the interrupted
program continues from where it left off.
Note that a simple RET instruction would also return
execution to the interrupted program, but it would have left
the interrupt control system thinking an interrupt was still in
progress, making future interrupts impossible.
Table 22
Vector addresses
SOURCE
IE0
SI
TF0
IE1
TF1
VECTOR ADDRESS
0003H
002BH
000BH
0013H
001BH
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