Rainbow Electronics ATmega103L - Manual (Page 76)

ATmega603/103
76
Figure 53. Port A Schematic Diagrams (Pins PA0 - PA7)
Port B
Port B is an 8-bit bi-directional I/O port with internal pull-ups.
Three I/O memory address locations are allocated for 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 20mA and thus drive LED dis-
plays directly. When pins PB0 to PB7 are used as inputs and are externally pulled low, they will source current if the
internal pull-up resistors are activated.
DA
T
A
BUS
D
D
Q
Q
RESET
RESET
C
C
WD
WP
RD
RP
MOS
PULL-
UP
PAn
R
R
WP:
WD:
RL:
RP:
RD:
SRE:
A:
D:
W:
R:
n: WRITE PORTA
WRITE DDRA
READ PORTA LATCH
READ PORTA PIN
READ DDRA
EXT. SRAM ENABLE
ADDRESS
DATA
WRITE
READ
0-7
DDAn
PORTAn
SRE
SRE
R
R
Dn
Dn
W
W
An
An
RL