Port b, Port b data register – portb, Port b data direction register – ddrb – Rainbow Electronics AT90LS8535 User Manual
Page 78: Port b input pins address – pinb
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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
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 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
7
6
5
4
3
2
1
0
$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
7
6
5
4
3
2
1
0
$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
7
6
5
4
3
2
1
0
$16 ($36)
PINB7
PINB6
PINB5
PINB4
PINB3
PINB2
PINB1
PINB0
PINB
Read/Write
R
R
R
R
R
R
R
R
Initial Value
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A