ATtiny44 datasheet(57/236 Pages) ATMEL

57 / 236 page

8006H–AVR–10/09

ATtiny24/44/84

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 indi-

cated by the two arrows tpd,max and tpd,min, a single signal transition on the pin will be delayed

between ½ and 1½ system clock period depending upon the time of assertion.

When reading back a software assigned pin value, a nop instruction must be inserted as indi-

cated in Figure 10-4 on page 57. The out instruction sets the “SYNC LATCH” signal at the

positive edge of the clock. In this case, the delay tpd through the synchronizer is one system

clock period.

Figure 10-4. Synchronization when Reading a Software Assigned Pin Value

The following code example shows how to set port A pins 0 and 1 high, 2 and 3 low, and define

the port pins from 4 to 5 as input with a pull-up assigned to port pin 4. The resulting pin values

are read back again, but as previously discussed, a nop instruction is included to be able to read

back the value recently assigned to some of the pins.

Note:

Two temporary registers are used to minimize the time from pull-ups are set on pins 0, 1 and 4,

until the direction bits are correctly set, defining bit 2 and 3 as low and redefining bits 0 and 1 as

strong high drivers.

Assembly Code Example

...

; Define pull-ups and set outputs high

; Define directions for port pins

ldi

r16,(1<<PA4)|(1<<PA1)|(1<<PA0)

ldi

r17,(1<<DDA3)|(1<<DDA2)|(1<<DDA1)|(1<<DDA0)

out

PORTA,r16

out

DDRA,r17

; Insert nop for synchronization

nop

; Read port pins

r16,PINA

...

out PORTx, r16

nop

in r17, PINx

0xFF

0x00

0xFF

SYSTEM CLK

r16

INSTRUCTIONS

SYNC LATCH

PINxn

r17

ATtiny44 Datasheet(PDF) 57 Page - ATMEL Corporation

ATtiny44 Datasheet(HTML) 57 Page - ATMEL Corporation

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 ...More

Datasheet Descarga

Enlace URL