Rainbow Electronics ATtiny2313 - Manual (Page 48)

48
ATtiny2313
2543A–AVR–08/03
Note that enabling the alternate function of some of the port pins does not affect the use
of the other pins in the port as general digital I/O.
Ports as General Digital
I/O The ports are bi-directional I/O ports with optional internal pull-ups. Figure 22 shows a
functional description of one I/O-port pin, here generically called Pxn.
Figure 22. General Digital I/O (1)
Note: 1. WRx, WPx, WDx, RRx, RPx, and RDx are common to all pins within the same port.
clk
I/O
, SLEEP, and PUD are common to all ports.
Configuring the Pin Each port pin consists of three register bits: DDxn, PORTxn, and PINxn. As shown in
“Register Description for I/O-Ports” on page 60, the DDxn bits are accessed at the
DDRx I/O address, the PORTxn bits at the PORTx I/O address, and the PINxn bits at
the PINx I/O address.
The DDxn bit in the DDRx Register selects the direction of this pin. If DDxn is written
logic one, Pxn is configured as an output pin. If DDxn is written logic zero, Pxn is config-
ured as an input pin.
If PORTxn is written logic one when the pin is configured as an input pin, the pull-up
resistor is activated. To switch the pull-up resistor off, PORTxn has to be written logic
zero or the pin has to be configured as an output pin. The port pins are tri-stated when
reset condition becomes active, even if no clocks are running.
If PORTxn is written logic one when the pin is configured as an output pin, the port pin is
driven high (one). If PORTxn is written logic zero when the pin is configured as an out-
put pin, the port pin is driven low (zero).
clk
RPx
RRx
RDx
WDx
PUD
SYNCHRONIZER
WDx: WRITE DDRx
WRx: WRITE PORTx
RRx: READ PORTx REGISTER
RPx: READ PORTx PIN
PUD: PULLUP DISABLE
clk
I/O
: I/O CLOCK
RDx: READ DDRx
D
L
Q
Q
RESET
RESET
Q
Q D
Q
Q D
CLR
PORTxn
Q
Q D
CLR
DDxn
PINxn
D
ATA
B
U
S
SLEEP
SLEEP: SLEEP CONTROL
Pxn
I/O
WPx
0
1
WRx
WPx: WRITE PINx REGISTER