参数资料
型号: AT89C51ED2-SMSUM
厂商: Atmel
文件页数: 3/137页
文件大小: 0K
描述: IC 8051 MCU FLASH 64K 68PLCC
产品培训模块: MCU Product Line Introduction
标准包装: 304
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: 68-PLCC
包装: 管件
配用: AT89OCD-01-ND - USB EMULATOR FOR AT8XC51 MCU
100
4235K–8051–05/08
AT89C51RD2/ED2
24.6.4
Bootloader Functionality
The bootloader can be activated by two means: Hardware conditions or regular boot process.
The Hardware conditions (EA = 1, PSEN = 0) during the Reset# falling edge force the on-chip
bootloader execution. This allows an application to be built that will normally execute the end
user’s code but can be manually forced into default ISP operation.
As PSEN is a an output port in normal operating mode after reset, user application should take
care to release PSEN after falling edge of reset signal. The hardware conditions are sampled at
reset signal falling edge, thus they can be released at any time when reset input is low.
To ensure correct microcontroller startup, the PSEN pin should not be tied to ground during
power-on (See Figure 24-4).
Figure 24-4. Hardware conditions typical sequence during power-on.
The on-chip bootloader boot process is shown Figure 24-5.
VCC
PSEN
RST
Table 24-6.
Bootloader Process Description
Purpose
Hardware Conditions
The Hardware Conditions force the bootloader execution whatever BLJB,
BSB and SBV values.
BLJB
The Boot Loader Jump Bit forces the application execution.
BLJB = 0 => Bootloader execution
BLJB = 1 => Application execution
The BLJB is a fuse bit in the Hardware Byte.
It can be modified by hardware (programmer) or by software (API).
Note: The BLJB test is performed by hardware to prevent any program
execution.
SBV
The Software Boot Vector contains the high address of customer bootloader
stored in the application.
SBV = FCh (default value) if no customer bootloader in user Flash.
Note: The customer bootloader is called by JMP [SBV]00h instruction.
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