AT90S/LS4434 and AT90S/LS8535
71
Port A Schematics
Note that all port pins are synchronized. The synchronization latch is, however, not shown in the figure.
Figure 51.
Port A Schematic Diagrams (Pins PA0 - PA7)
Port B
Port B is an 8-bit bi-directional I/O port.
Three I/O memory address locations are allocated for the Port B, one each for the Data Register – PORTB, $18($38), Data
Direction Register – DDRB, $17($37) and the Port B Input Pins – PINB, $16($36). The Port B Input Pins address is read-
only, while the Data Register and the Data Direction Register are read/write.
All port pins have individually selectable pull-up resistors. The Port B output buffers can sink 20 mA and thus drive LED dis-
plays directly. When pins PB0 to PB7 are used as inputs and are externally pulled low, they will source current if the
internal pull-up resistors are activated.
The Port B pins with alternate functions are shown in Table 31.
Table 31.
Port B Pin Alternate Functions
Port Pin
Alternate Functions
PB0
T0 (Timer/Counter0 External Counter Input)
PB1
T1 (Timer/Counter1 External Counter Input)
PB2
AIN0 (Analog Comparator Positive Input)
PB3
AIN1 (Analog Comparator Negative Input)
PB4
SS (SPI Slave Select Input)
PB5
MOSI (SPI Bus Master Output/Slave Input)
PB6
MISO (SPI Bus Master Input/Slave Output)
PB7
SCK (SPI Bus Serial Clock)
DA
T
A
BUS
D
D
Q
Q
RESET
RESET
C
C
WD
WP
RD
MOS
PULL-
UP
PDn
ADCn
TO ADC MUX
WP:
WD:
RL:
RP:
RD:
n:
WRITE PORTA
WRITE DDRA
READ PORTA LATCH
READ PORTA PIN
READ DDRA
0-7
DDAn
PORTAn
RL
RP
PWRDN