AT90S4414/8515
57
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 the following table:
When the pins are used for the alternate function the DDRB and PORTB register has 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 21. Port B Pins Alternate Functions
Port Pin Alternate Functions
PB0 T0 (Timer/Counter 0 external counter input)
PB1 T1 (Timer/Counter 1 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/Write RRRRRRRR
Initial value Hi-Z Hi-Z Hi-Z Hi-Z Hi-Z Hi-Z Hi-Z Hi-Z
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