DS89C420 Dallas Semiconducotr, DS89C420 Datasheet - Page 6

• Manufacturer Part Number: DS89C420
• Description: Ultra-High-Speed Microcontroller
• Manufacturer: Dallas Semiconducotr

10–17
DIP
10
11
12
13
14
15
16
17
31
PLCC
11, 13–
PIN
19
11
13
14
15
16
17
18
19
35
5, 7–13
TQFP
10
11
12
13
29
5
7
8
9
P3.0–P3.7
NAME
P3.0
P3.1
P3.2
P3.3
P3.4
P3.5
P3.6
P3.7
EA
Port 3, I/O. Port 3 functions as both an 8-bit, bidirectional I/O
port and an alternate functional interface for external interrupts,
serial port 0, timer 0 and 1 inputs, and
reset condition of port 3 is with all bits at a logic 1. In this state,
a weak pullup holds the port high. This condition also serves as
an input mode, since any external circuit that writes to the port
overcomes the weak pullup. When software writes a 0 to any
port pin, the DS89C420 activates a strong pulldown that
remains on until either a 1 is written or a reset occurs. Writing a
1 after the port has been at 0 causes a strong transition driver to
turn on, followed by a weaker sustaining pullup. Once the
momentary strong driver turns off, the port again becomes both
the output high and input state. The alternate modes of Port 3
are outlined below.
PORT
P3.0
P3.1
P3.2
P3.3
P3.4
P3.5
P3.6
P3.7
External Access. Allows selection of internal or external
program memory. Connect to ground to force the DS89C420 to
use an external memory-program memory. The internal RAM
is still accessible as determined by register settings. Connect to
V
6 of 59
CC
to use internal flash memory.
ALTERNATE FUNCTION
RXD0 Serial Port 0 Receive
TXD0 Serial Port 0 Transmit
T0
T1
INT0
INT1
WR
RD
External Interrupt 0
External Interrupt 1
External Data Memory Write Strobe
External Data Memory Read Strobe
Timer 0 External Input
Timer 1 External Input
FUNCTION
RD
and
WR
strobes. The