P89C51RB2BA datasheet(40/52 Pages) PHILIPS

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Philips Semiconductors

Preliminary specification

89C51RB2/89C51RC2/

89C51RD2

80C51 8-bit Flash microcontroller family

16KB/32KB/64KB ISP/IAP Flash with 512B/512B/1KB RAM

1999 Sep 23

FFFF

C000

8000

4000

2000

0000

BLOCK 4

16 kB

BLOCK 3

16 kB

BLOCK 2

16 kB

BLOCK 1

8 kB

BLOCK 0

8 kB

PROGRAM

ADDRESS

BOOT ROM

(1 kB)

FFFF

FC00

SU01298

89C51RD2

89C51RC2

89C51RB2

Figure 43. Flash Memory Configurations

Power-On Reset Code Execution

The 89C51RB2/RC2/RD2 contains two special Flash registers: the

BOOT VECTOR and the STATUS BYTE. At the falling edge of reset,

the 89C51RB2/RC2/RD2 examines the contents of the Status Byte.

If the Status Byte is set to zero, power-up execution starts at

location 0000H, which is the normal start address of the user’s

application code. When the Status Byte is set to a value other than

zero, the contents of the Boot Vector is used as the high byte of the

execution address and the low byte is set to 00H. The factory

default setting is 0FCH, corresponds to the address 0FC00H for the

factory masked-ROM ISP boot loader. A custom boot loader can be

written with the Boot Vector set to the custom boot loader.

NOTE:

When erasing the Status Byte or Boot Vector,

both bytes are erased at the same time. It is necessary

to reprogram the Boot Vector after erasing and

updating the Status Byte.

Hardware Activation of the Boot Loader

The boot loader can also be executed by holding PSEN LOW,

EA greater than VIH (such as +5 V), and ALE HIGH (or not connected)

at the falling edge of RESET. This is the same effect as having a

non-zero status byte. This allows an application to be built that will

normally execute the end user’s code but can be manually forced

into ISP operation.

If the factory default setting for the Boot Vector (0FCH) is changed, it

will no longer point to the ISP masked-ROM boot loader code. If this

happens, the only way it is possible to change the contents of the

Boot Vector is through the parallel programming method, provided

that the end user application does not contain a customized loader

that provides for erasing and reprogramming of the Boot Vector and

Status Byte.

After programming the Flash, the status byte should be programmed

to zero in order to allow execution of the user’s application code

beginning at address 0000H.

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