DS89C420_05 Datasheet, PDF (13/47 Pages) Maxim Integrated Products – Ultra-High-Speed Microcontroller

DS89C420 Ultra-High-Speed Microcontroller
PIN DESCRIPTION (continued)
PIN
NAME
DIP
PLCC
TQFP
21
24
18
P2.0 (A8)
22
25
19
P2.1 (A9)
23
26
20
P2.2 (A10)
24
27
21
P2.3 (A11)
25
28
22
P2.4 (A12)
26
29
23
P2.5 (A13)
27
30
24
P2.6 (A14)
28
31
25
P2.7 (A15)
10–17
11, 13–19 5, 7–13
P3.0–P3.7
10
11
5
P3.0
11
13
7
P3.1
12
14
8
P3.2
13
15
9
P3.3
14
16
10
P3.4
15
17
11
P3.5
16
18
12
P3.6
17
19
13
P3.7
31
35
29
EA
FUNCTION
Port 2 (A8–15), I/O. Port 2 is an 8-bit, bidirectional I/O port. The reset
condition of port 2 is logic high. 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. As an alternate function, port 2 can
function as the MSB of the external address bus when reading external
program memory and read/write external RAM or peripherals. In page mode
1, port 2 provides both the MSB and LSB of the external address bus; in page
mode 2, it provides the MSB and data.
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
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
ALTERNATE
RXD0
FUNCTION
Serial Port 0 Receive
P3.1
P3.2
P3.3
TXD0
INT0
INT1
Serial Port 0 Transmit
External Interrupt 0
External Interrupt 1
P3.4
T0
Timer 0 External Input
P3.5
T1
P3.6
WR
Timer 1 External Input
External Data Memory Write Strobe
P3.7
RD
External Data Memory Read Strobe
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 VCC to use internal flash memory.
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