AT90S4414/8515
58
PortB as General Digital I/O
All 8 pins in port B have equal functionality when used as digital I/O pins.
PBn, General I/O pin: The DDBn bit in the DDRB register selects the direction of this pin, if DDBn is set (one), PBn is con-
figured as an output pin. If DDBn is cleared (zero), PBn is configured as an input pin. If PORTBn is set (one) when the pin
configured as an input pin, the MOS pull up resistor is activated. To switch the pull up resistor off, the PORTBn has to be
cleared (zero) or the pin has to be configured as an output pin. The Port B pins are tri-stated when a reset condition
becomes active, even if the clock is not active.
n: 7,6…0, pin number.
Alternate Functions of PortB
The alternate pin configuration is as follows:
•
SCK - Port B, Bit 7
SCK: Master clock output, slave clock input pin for SPI channel. When the SPI is enabled as a slave, this pin is configured
as an input regardless of the setting of DDB7. When the SPI is enabled as a master, the data direction of this pin is con-
trolled by DDB7. When the pin is forced to be an input, the pull-up can still be controlled by the PORTB7 bit. See the
description of the SPI port for further details.
•
MISO - Port B, Bit 6
MISO: Master data input, slave data output pin for SPI channel. When the SPI is enabled as a master, this pin is configured
as an input regardless of the setting of DDB6. When the SPI is enabled as a slave, the data direction of this pin is controlled
by DDB6. When the pin is forced to be an input, the pull-up can still be controlled by the PORTB6 bit. See the description of
the SPI port for further details.
•
MOSI - Port B, Bit 5
MOSI: SPI Master data output, slave data input for SPI channel. When the SPI is enabled as a slave, this pin is configured
as an input regardless of the setting of DDB5. When the SPI is enabled as a master, the data direction of this pin is con-
trolled by DDB5. When the pin is forced to be an input, the pull-up can still be controlled by the PORTB5 bit. See the
description of the SPI port for further details.
•
SS - Port B, Bit 4
SS: Slave port select input. When the SPI is enabled as a slave, this pin is configured as an input regardless of the setting
of DDB4. As a slave, the SPI is activated when this pin is driven low. When the SPI is enabled as a master, the data direc-
tion of this pin is controlled by DDB4. When the pin is forced to be an input, the pull-up can still be controlled by the
PORTB4 bit. See the description of the SPI port for further details.
•
AIN1 - Port B, Bit 3
AIN1, Analog Comparator Negative Input. When configured as an input (DDB3 is cleared (zero)) and with the internal MOS
pull up resistor switched off (PB3 is cleared (zero)), this pin also serves as the negative input of the on-chip analog
comparator.
•
AIN0 - Port B, Bit 2
AIN0, Analog Comparator Positive Input. When configured as an input (DDB2 is cleared (zero)) and with the internal MOS
pull up resistor switched off (PB2 is cleared (zero)), this pin also serves as the positive input of the on-chip analog
comparator.
•
T1 - Port B, Bit 1
T1, Timer/Counter1 counter source. See the timer description for further details
•
T0 - Port B, Bit 0
T0: Timer/Counter0 counter source. See the timer description for further details.
Table 22. DDBn Effects on Port B Pins
DDBn
PORTBn
I/O
Pull up
Comment
0
0
Input
No
Tri-state (Hi-Z)
0
1
Input
Yes
PBn will source current if ext. pulled low.
1
0
Output
No
Push-pull Zero Output
1
1
Output
No
Push-pull One Output