Rainbow Electronics AT90LS8535 - Manual (Page 78)

78
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