Datasheet

4235K–8051–05/08

AT89C51RD2/ED2

24. Flash/EEPROM Memory

The Flash memory increases EEPROM and ROM functionality with in-circuit electrical erasure

and programming. It contains 64K bytes of program memory organized respectively in 512

pages of 128 bytes. This memory is both parallel and serial In-System Programmable (ISP). ISP

allows devices to alter their own program memory in the actual end product under software con-

trol. A default serial loader (bootloader) program allows ISP of the Flash.

The programming does not require external dedicated programming voltage. The necessary

high programming voltage is generated on-chip using the standard V

pins of the

microcontroller.

24.1 Features

• Flash EEPROM Internal Program Memory

• Boot vector allows user provided Flash loader code to reside anywhere in the Flash memory

space. This configuration provides flexibility to the user.

• Default loader in Boot ROM allows programming via the serial port without the need of a user

provided loader.

• Up to 64K bytes external program memory if the internal program memory is disabled (EA =

0).

• Programming and erasing voltage with standard power supply

• Read/Programming/Erase:

– Byte-wise read without wait state

– Byte or page erase and programming (10 ms)

• Typical programming time (64K bytes) is 22s with on chip serial bootloader

• Parallel programming with 87C51 compatible hardware interface to programmer

• Programmable security for the code in the Flash

• 100K write cycles

• 10 years data retention

24.2 Flash Programming and Erasure

The 64-K byte Flash is programmed by bytes or by pages of 128 bytes. It is not necessary to

erase a byte or a page before programming. The programming of a byte or a page includes a

self erase before programming.

There are three methods of programming the Flash memory:

1. The on-chip ISP bootloader may be invoked which will use low level routines to pro-

gram the pages. The interface used for serial downloading of Flash is the UART.

2. The Flash may be programmed or erased in the end-user application by calling low-

level routines through a common entry point in the Boot ROM.

3. The Flash may be programmed using the parallel method by using a conventional

EPROM programmer. The parallel programming method used by these devices is simi-

lar to that used by EPROM 87C51 but it is not identical and the commercially available

programmers need to have support for the AT89C51RD2/ED2. The bootloader and the

Application Programming Interface (API) routines are located in the BOOT ROM.