P89C51RC datasheet(39/50 Pages) PHILIPS

39 / 50 page

Philips Semiconductors

Product specification

P89C51RC+/P89C51RD+

80C51 8-bit Flash microcontroller family

32K/64K ISP FLASH with 512–1K RAM

1999 Oct 27

FFFF

C000

8000

4000

2000

0000

BLOCK 4

16k BYTES

BLOCK 3

16k BYTES

BLOCK 2

16k BYTES

BLOCK 1

8k BYTES

BLOCK 0

8k BYTES

PROGRAM

ADDRESS

89C51RC+

89C51RD+

BOOT ROM

(1k BYTES ON

ALL PARTS)

FFFF

FC00

SU01041

Figure 41. FLASH Memory Configurations

Power-On Reset Code Execution

The 89C51RX+ contains two special FLASH registers: the BOOT

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

89C51RX+ 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 +12 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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