参数资料
型号: AT89C51ED2-RDRUM
厂商: Atmel
文件页数: 44/137页
文件大小: 0K
描述: IC MCU FLASH 8051 64K 5V 64-VQFP
产品培训模块: MCU Product Line Introduction
标准包装: 1
系列: 89C
核心处理器: 8051
芯体尺寸: 8-位
速度: 60MHz
连通性: SPI,UART/USART
外围设备: POR,PWM,WDT
输入/输出数: 50
程序存储器容量: 64KB(64K x 8)
程序存储器类型: 闪存
EEPROM 大小: 2K x 8
RAM 容量: 2K x 8
电压 - 电源 (Vcc/Vdd): 2.7 V ~ 5.5 V
振荡器型: 外部
工作温度: -40°C ~ 85°C
封装/外壳: 44-LQFP
包装: 标准包装
其它名称: AT89C51ED2-RDRUMDKR
14
4235K–8051–05/08
AT89C51RD2/ED2
5.
Port Types
AT89C51RD2/ED2 I/O ports (P1, P2, P3, P4, P5) implement the quasi-bidirectional output that
is common on the 80C51 and most of its derivatives. This output type can be used as both 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 pulled low, it is driven strongly and able to sink a fairly large current. These features are
somewhat similar to an open drain output except that there are three pull-up transistors in the
quasi-bidirectional output that serve different purposes. One of these pull-ups, called the "weak"
pull-up, is turned on whenever the port latch for the pin contains a logic 1. The 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 "medium" 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-bidi-
rectional pin that is outputting a 1. If a pin that has a logic 1 on it is pulled low by an external
device, the medium pull-up turns off, and only the 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
medium pull-up and take the voltage on the port pin below its input threshold.
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 a brief time, two CPU clocks, in order to
pull the port pin high quickly. Then it turns off again.
The DPU bit (bit 7 in AUXR register) allows to disable the permanent weak pull up of all ports
when latch data is logical 0.
The quasi-bidirectional port configuration is shown in Figure 5-1.
Figure 5-1.
Quasi-Bidirectional Output
2 CPU
Input
Pin
Strong
Medium
N
Weak
P
Clock Delay
Port Latch
Data
DPU
AUXR.7
P
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