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SH79F3283
64
7.9.9 External Interrupt Inputs
The SH79F3283 has 5 external interrupt inputs. External interrupt0-3 each has one vector address. External interrupt 4 has 8
inputs; all of them share one vector address. These external interrupts can be programmed to be level-triggered or
edge-triggered by clearing or setting bit IT1 or IT0 in register TCON and register EXF1. If ITn = 0 (n = 0 - 1), external interrupt
0/1 is triggered by a low level detected at the INT0/1 pin. If ITn = 1 (n = 0 - 1), external interrupt 0/1 is edge triggered. In this
mode if consecutive samples of the INT0/1 pin show a high level in one cycle and a low level in the next cycle, interrupt
request flag in register r EXF1 is set, causing an interrupt request. Since the external interrupt pins are sampled once each
machine cycle, an input high or low level should be held for at least one machine cycle to ensure proper sampling.
If the external interrupt is edge-triggered, the external source has to hold the request pin high for at least one machine cycle,
and then hold it low for at least one machine cycle. This is to ensure that the transition is detected and that interrupt request
flag is set. Notice that IE0-1 is automatically cleared by CPU when the service routine is called while IF4x should be cleared by
software. External interrupt4 operates in the similar ways except have different registers and have more selection of trigger.
If the external interrupt is level-triggered, the external source must hold the request active until the requested interrupt is
generated, which will take 2 machine cycles. If the external interrupt is still asserted when the interrupt service routine is
completed, another interrupt will be generated. It is not necessary to clear the interrupt flag IEx (x = 0, 1, 2, 3) when the
interrupt is level sensitive, it simply tracks the input pin level.
In order to satisfy the different request interrupt response, there can set sample clock Prescaler Select bits and sample times
Select bits in EXCON register
Sample clock Prescaler Select bits and sample times Select bits in EXCON register are invalid in the IDLE and Power-Down
mode.
If an external interrupt is enabled when the SH79F3283 is put into Power down or Idle mode, the interrupt occurrence will
cause the processor to wake up and resume operation.
IEi
The Block Diagram of INTi
Interrupt
Request
Flag
System Clock
IxSN[1:0],x=0,1
INTi
PxCR
x=0,2,3,4
Sampling
00
01
10
11
ITi[1:0], i=2-4
0
1
ITi[1:0], i=0-1
Sampling Num
1,2,3,4
Prescaler
1,4,16,64
IxPS[1:0],x=0,1
Note: The INT0/1/2/3 interrupt flag will be cleared by hardware, but IF40-IF47 must be cleared by software
SN Sampling Cyle
> SN Sampling Cycle
High-Level Threshold
Low-Level Threshold
Low-Level Threshold
>2*SN Sampling Cycle
(SN=1,2,3,4)
(SN=1,2,3,4)
(SN=1,2,3,4)
External Interrupt Detecting