4. Parts are guaranteed to operate down to 0 Hz.

EXPLANATION OF THE AC SYMBOLS

Each timing symbol has five characters. The first character is always ‘t’ (= time). The other characters, depending on their positions, indicate the name of a signal or the logical status of that signal. The designations are:

A – Address

C – Clock

D – Input data

H – Logic level high

I – Instruction (program memory contents)

L – Logic level low, or ALE

P – PSEN

Q – Output data

R–RD signal

t – Time

V – Valid

W– WR signal

X – No longer a valid logic level

Z – Float

Examples: tAVLL = Time for address valid to ALE low.

tLLPL =Time for ALE low to PSEN low.

Security

The security feature protects against software piracy and prevents the contents of the FLASH from being read. The Security Lock bits are located in FLASH. The 89C51/89C52/89C54/89C58 has 3 programmable security lock bits that will provide different levels of protection for the on-chip code and data (see Table 8). Unlike the ROM and OTP versions, the security lock bits are independent. LB3 includes the security protection of LB1.

Definitions

Short-form specification — The data in a short-form specification is extracted from a full data sheet with the same type number and title. For detailed information see the relevant data sheet or data handbook.

Limiting values definition — Limiting values given are in accordance with the Absolute Maximum Rating System (IEC 134). Stress above one or more of the limiting values may cause permanent damage to the device. These are stress ratings only and operation of the device at these or at any other conditions above those given in the Characteristics sections of the specification is not implied. Exposure to limiting values for extended periods may affect device reliability.

Application information — Applications that are described herein for any of these products are for illustrative purposes only. Philips Semiconductors make no representation or warranty that such applications will be suitable for the specified use without further testing or modification.

Disclaimers

Life support — These products are not designed for use in life support appliances, devices or systems where malfunction of these products can reasonably be expected to result in personal injury. Philips Semiconductors customers using or selling these products for use in such applications do so at their own risk and agree to fully indemnify Philips Semiconductors for any damages resulting from such application.

Right to make changes — Philips Semiconductors reserves the right to make changes, without notice, in the products, including circuits, standard cells, and/or software, described or contained herein in order to improve design and/or performance. Philips Semiconductors assumes no responsibility or liability for the use of any of these products, conveys no license or title under any patent, copyright, or mask work right to these products, and makes no representations or warranties that these products are free from patent, copyright, or mask work right infringement, unless otherwise specified.

增强的通用异步收发机（UART）

    通用异步收发机（UART）在第一部分介绍的数据手册IC20,80C51-Based的8位微控制器中的所有正常模式都可运行。此外，通用异步收发机（UART）可以通过寻找失踪停止位来实现成帧误差的寻找，同时实现自动地址识别。该通用异步收发机（UART）和标准80C51通用异步收发机（UART）一样，也完全支持多处理器沟通。

    当用来作帧误差寻找时，在通讯中，通用异步收发机（UART）是通过寻找失踪停止位来实现的。失踪位将设置在SCON寄存器的FE位。该FE位和SM0共用SCON.7位，而SCON.7的功能由PCON.6决定(SMOD0)（见图7)。SMOD0功能设置完成后，SCON.7与FE实现相同的功能。当SMOD0被清除时，SCON.7与SM0实现相同功能。当用作FE时，SCON.7只能通过软件清除。参考图8。 闪存微控制器英文文献和中文翻译(4):http://www.youerw.com/fanyi/lunwen_49448.html