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AT89LP51 数据表(PDF) 41 Page - ATMEL Corporation

部件名 AT89LP51
功能描述  8-bit Microcontroller with 4K/8K Bytes In-System Programmable Flash
PDF  113 Pages
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制造商  ATMEL [ATMEL Corporation]
网页  http://www.atmel.com
标志 ATMEL - ATMEL Corporation

AT89LP51 数据表(HTML) 41 Page - ATMEL Corporation

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41
3709C–MICRO–5/11
AT89LP51/52 - Preliminary
10. I/O Ports
The AT89LP51/52 can be configured for between 32 and 36 I/O pins. The exact number of I/O
pins available depends on the clock, external memory and package type as shown in Table 10-
1.
10.1
Port Configuration
Each 8-bit port on the AT89LP51/52 may be configured in one of four modes: quasi-bidirectional
(standard 8051 port outputs), push-pull output, open-drain output, or input-only. Port modes may
be assigned in software on a port-by-port basis as shown in Table 10-2 using the PMOD register
listed in Table 10-3. The Tristate-Port User Fuse determines the default state of the port pins
(See “User Configuration Fuses” on page 86). When the fuse is enabled, all port pins default to
input-only mode after reset. When the fuse is disabled, all port pins on P1, P2 and P3 default to
quasi-bidirectional mode after reset and are weakly pulled high. P0 is set to Open-drain mode.
P4 always operates in quasi-bidirectional mode.
Each port pin also has a Schmitt-triggered input for improved input noise rejection. During
Power-down all the Schmitt-triggered inputs are disabled with the exception of P3.2 (INT0), P3.3
(INT1), RST, P4.6 (XTAL1) and P4.7 (XTAL2). Therefore, P3.2, P3.3, P4.6 and P4.7 should not
be left floating during Power-down.
.
Table 10-1.
I/O Pin Configurations
Clock Source
External Program Access
External Data Access
Number of I/O
Pins
External Crystal or
Resonator
Yes (PSEN+ALE+P0+P2)
Yes (RD+WR)
14
No
16
No
Yes (ALE+RD+WR+P0)
31
No
34
External Clock
Yes (PSEN+ALE+P0+P2)
Yes (RD+WR)
15
No
17
No
Yes (ALE+RD+WR+P0)
32
No
35
Internal RC
Oscillator
Yes (PSEN+ALE+P0+P2)
Yes (RD+WR)
16
No
18
No
Yes (ALE+RD+WR+P0)
33
No
36
Table 10-2.
Configuration Modes for Port x
PxM0
PxM1
Port Mode
00
Quasi-bidirectional
01
Push-pull Output
10
Input Only (High Impedance)
1
1
Open-Drain Output



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