參數(shù)資料
型號: AT89LP428-20PU
廠商: Atmel
文件頁數(shù): 80/149頁
文件大?。?/td> 0K
描述: MCU 8051 4K FLASH SPI 28PDIP
產(chǎn)品培訓(xùn)模塊: MCU Product Line Introduction
標(biāo)準(zhǔn)包裝: 14
系列: 89LP
核心處理器: 8051
芯體尺寸: 8-位
速度: 20MHz
連通性: SPI,UART/USART
外圍設(shè)備: 欠壓檢測/復(fù)位,POR,PWM,WDT
輸入/輸出數(shù): 30
程序存儲器容量: 4KB(4K x 8)
程序存儲器類型: 閃存
EEPROM 大?。?/td> 512 x 8
RAM 容量: 768 x 8
電壓 - 電源 (Vcc/Vdd): 2.4 V ~ 5.5 V
振蕩器型: 內(nèi)部
工作溫度: -40°C ~ 85°C
封裝/外殼: 28-DIP(0.300",7.62mm)
包裝: 管件
36
3654A–MICRO–8/09
AT89LP428/828
10.1.1
Quasi-bidirectional Output
Port pins in quasi-bidirectional output mode function similar to standard 8051 port pins. A Quasi-
bidirectional port can be used both as an input and output without the need to reconfigure the
port. This is possible because when the port outputs a logic high, it is weakly driven, allowing an
external device to pull the pin low. When the pin is driven low, it is driven strongly and able to
sink a large current. There are three pull-up transistors in the quasi-bidirectional output that
serve different purposes.
One of these pull-ups, called the “very weak” pull-up, is turned on whenever the port latch for the
pin contains a logic “1”. This very weak pull-up sources a very small current that will pull the pin
high if it is left floating.
A second pull-up, called the “weak” pull-up, is turned on when the port latch for the pin contains
a logic “1” and the pin itself is also at a logic “1” level. This pull-up provides the primary source
current for a quasi-bidirectional pin that is outputting a “1”. If this pin is pulled low by an external
device, this weak pull-up turns off, and only the very weak pull-up remains on. In order to pull the
pin low under these conditions, the external device has to sink enough current to overpower the
weak pull-up and pull the port pin below its input threshold voltage.
The third pull-up is referred to as the “strong” pull-up. This pull-up is used to speed up low-to-
high transitions on a quasi-bidirectional port pin when the port latch changes from a logic “0” to a
logic “1”. When this occurs, the strong pull-up turns on for two CPU clocks quickly pulling the
port pin high. The quasi-bidirectional port configuration is shown in Figure 10-1.
Figure 10-1. Quasi-bidirectional Output
Table 10-3.
Port Configuration Registers
Port
Port Data
Port Configuration
1
P1 (90H)
P1M0 (C2H), P1M1 (C3H)
2
P2 (A0H)
P2M0 (C4H), P2M1 (C5H)
3
P3 (B0H)
P3M0 (C6H), P3M1 (C7H)
4
P4 (C0H)
P4M0 (BEH), P4M1 (BFH)
1 Clock Delay
(D Flip-Flop)
Strong
Very
Weak
Port
Pin
VCC
From Port
Register
Input
Data
PWD
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