DS89C420_02 Datasheet, PDF (6/58 Pages) Maxim Integrated Products – Ultra-High-Speed Microcontroller

DIP
10–17
PIN
PLCC
11, 13–
19
NAME
TQFP
5, 7–13 P3.0–P3.7
FUNCTION
DS89C420
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 ^RD and WR strobes. The
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 ALTERNATE FUNCTION
10
11
5
P3.0 P3.0 RXD0 Serial Port 0 Receive
11
13
7
P3.1 ^{P3.1 TXD0 Serial Port 0 Transmit}
12
14
8
P3.2 ^{P3.2 INT0 External Interrupt 0}
13
15
9
P3.3 ^{P3.3 INT1 External Interrupt 1}
14
16
10
P3.4 ^{P3.4 T0 Timer 0 External Input}
15
17
11
P3.5
P3.5 T1 Timer 1 External Input
16
18
12
P3.6
P3.6
WR External Data Memory Write Strobe
17
19
13
P3.7
P3.7
RD _{External Data Memory Read Strobe}
31
35
29
EA
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_CC to use internal flash memory.
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