Manual

AT90S/LS8535

1041H–11/01

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

Input Pins – PINB, $16($36). The Port B Input Pins address is read-only, while the Data

All port pins have individually selectable pull-up resistors. The Port B output buffers can

sink 20 mA and thus drive LED displays directly. When pins PB0 to PB7 are used as

inputs and are externally pulled low, they will source current if the internal pull-up resis-

tors are activated.

The Port B pins with alternate functions are shown in Table 30.

When the pins are used for the alternate function, the DDRB and PORTB registers have

to be set according to the alternate function description.

Port B Data Register – PORTB

Port B Data Direction Register

– DDRB

Port B Input Pins Address –

PINB

The Port B Input Pins address (PINB) is not a register and this address enables access

to the physical value on each Port B pin. When reading PORTB, the Port B Data Latch

is read and when reading PINB, the logical values present on the pins are read.

Table 30. 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)

Bit 76543210

$18 ($38)

PORTB7 PORTB6 PORTB5 PORTB4 PORTB3 PORTB2 PORTB1 PORTB0 PORTB

Read/Write R/W R/W R/W R/W R/W R/W R/W R/W

Initial Value 0 0 0 0 0 0 0 0

Bit 76543210

$17 ($37) DDB7 DDB6 DDB5 DDB4 DDB3 DDB2 DDB1 DDB0 DDRB

Read/Write R/W R/W R/W R/W R/W R/W R/W R/W

Initial Value 0 0 0 0 0 0 0 0

Bit 76543210

$16 ($36) PINB7 PINB6 PINB5 PINB4 PINB3 PINB2 PINB1 PINB0 PINB

Read/WriteRRRRRRRR

Initial Value N/A N/A N/A N/A N/A N/A N/A N/A