Rainbow Electronics AT90LS4433 - Manual (Page 82)

82
AT90S/LS4433
1042G–AVR–09/02
• TXD – Port D, Bit 1
Transmit Data (Data Output pin for the UART). When the UART Transmitter is enabled,
this pin is configured as an output, regardless of the value of DDD1.
• RXD – Port D, Bit 0
Receive Data (Data Input pin for the UART). When the UART Receiver is enabled, this
pin is configured as an input, regardless of the value of DDD0. When the UART forces
this pin to be an input, a logical “1” in PORTD0 will turn on the internal pull-up.
Port D Schematics Note that all port pins are synchronized. The synchronization latches are, however, not
shown in the figures.
Figure 57. Port D Schematic Diagram (Pin PD0)
DA
T
A
BUS
D
D
Q
Q
RESET
RESET
C
C
WD
WP
RD
MOS
PULL-
UP
PD0
RXD
RXEN WP:
WD:
RL:
RP:
RD:
RXD:
RXEN: WRITE PORTD
WRITE DDRD
READ PORTD LATCH
READ PORTD PIN
READ DDRD
UART RECEIVE DATA
UART RECEIVE ENABLE
DDD0
PORTD0
RL
RP