52
AT90S2313
0839G–08/01
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 unintention-
ally 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 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 17.
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 17. Port B Pin Alternate Functions
Port Pin Alternate Functions
PB0 AIN0 (Analog comparator positive input)
PB1 AIN1 (Analog comparator negative input)
PB3 OC1 (Timer/Counter1 Output compare match output)
PB5 MOSI (Data input line for memory downloading)
PB6 MISO (Data output line for memory uploading)
PB7 SCK (Serial clock input)
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
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