DS89C420 Dallas Semiconducotr, DS89C420 Datasheet - Page 5

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

DIP
1–8
21
22
23
24
25
26
27
28
1
2
3
4
5
6
7
8
PLCC
PIN
2–9
24
25
26
27
28
29
30
31
2
3
4
5
6
7
8
9
TQFP
40–44
40
41
42
43
44
18
19
20
21
22
23
24
25
1
2
3
1
2
3
P2.0 (A8)
P2.1 (A9)
P2.2 (A10)
P2.3 (A11)
P2.4 (A12)
P2.5 (A13)
P2.6 (A14)
P2.7 (A15)
P1.0–P1.7 Port 1, I/O. Port 1 functions as both an 8-bit, bidirectional I/O
NAME
port and an alternate functional interface for timer 2 I/O, new
external interrupts, and new serial port 1. The reset condition of
port 1 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 state,
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 the output high
(and input) state. The alternate functions of Port 1 are outlined
below.
PORT
P1.0
P1.1
P1.2
P1.3
P1.4
P1.5
P1.6
P1.7
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.
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ALTERNATE FUNCTION
T2
T2EX Timer 2 Capture/Reload Trigger
RXD1 Serial Port 1 Receive
TXD1 Serial Port 1 Transmit
INT2 External Interrupt 2 (Positive Edge Detect)
INT4 External Interrupt 4 (Positive Edge Detect)
INT3
INT5
External I/O for Timer/Counter2
External Interrupt 3 (Negative Edge Detect)
External Interrupt 5 (Negative Edge Detect)
FUNCTION