Rainbow Electronics AT90LS4433 - Manual (Page 72)

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AT90S/LS4433
1042G–AVR–09/02
I/O Ports
All AVR ports have true Read-Modify-Write functionality when used as general digital
I/O ports. This means that the direction of one port pin can be changed without uninten-
tionally changing the direction of any other pin with the SBI and CBI instructions. The
same applies for changing drive value (if configured as output) or enabling/disabling of
pull-up resistors (if configured as input).
Port B Port B is a 6-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 23.
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
Table 23. Port B Pin Alternate Functions
Port Pin Alternate Functions
PB0 ICP (Timer/Counter1 Input Capture Pin)
PB1 OC1 (Timer/Counter1 Output Compare Match Output)
PB2 SS (SPI Slave Select Input)
PB3 MOSI (SPI Bus Master Output/Slave Input)
PB4 MISO (SPI Bus Master Input/Slave Output)
PB5 SCK (SPI Bus Serial Clock)
Bit 7 6 5 4 3 2 1 0
$18 ($38) – – PORTB5 PORTB4 PORTB3 PORTB2 PORTB1 PORTB0 PORTB
Read/Write R R 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) – – DDB5 DDB4 DDB3 DDB2 DDB1 DDB0 DDRB
Read/Write R R 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) – – PINB5 PINB4 PINB3 PINB2 PINB1 PINB0 PINB
Read/Write R R R R R R R R
Initial Value 0 0 N/A N/A N/A N/A N/A N/A