參數(shù)資料
型號: MC80C32-30SHXXX:D
廠商: TEMIC SEMICONDUCTORS
元件分類: 微控制器/微處理器
英文描述: 8-BIT, 30 MHz, MICROCONTROLLER, CDIP40
文件頁數(shù): 66/109頁
文件大?。?/td> 10824K
45
ATtiny20 [DATASHEET]
8235E–AVR–03/2013
Figure 10-3. Switching Between Input and Output in Break-Before-Make-Mode
10.2.4 Reading the Pin Value
Independent of the setting of Data Direction bit DDxn, the port pin can be read through the PINxn Register bit. As shown
in Figure 10-2 on page 43, the PINxn Register bit and the preceding latch constitute a synchronizer. This is needed to
avoid metastability if the physical pin changes value near the edge of the internal clock, but it also introduces a delay.
Figure 10-4 shows a timing diagram of the synchronization when reading an externally applied pin value. The maximum
and minimum propagation delays are denoted tpd,max and tpd,min respectively.
Figure 10-4. Synchronization when Reading an Externally Applied Pin value
Consider the clock period starting shortly after the first falling edge of the system clock. The latch is closed when the
clock is low, and goes transparent when the clock is high, as indicated by the shaded region of the “SYNC LATCH”
signal. The signal value is latched when the system clock goes low. It is clocked into the PINxn Register at the
succeeding positive clock edge. As indicated by the two arrows tpd,max and tpd,min, a single signal transition on the pin
will be delayed between and 1 system clock period depending upon the time of assertion.
out DDRx, r16
nop
0x02
0x01
SYSTEM CLK
INSTRUCTIONS
DDRx
intermediate tri-state cycle
out DDRx, r17
0x55
PORTx
0x01
intermediate tri-state cycle
Px0
Px1
tri-state
0x01
r17
0x02
r16
XXX
in r17, PINx
0x00
0xFF
INSTRUCTIONS
SYNC LATCH
PINxn
r17
XXX
SYSTEM CLK
t
pd, max
t pd, min
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