P89LPC954 datasheet(46/69 Pages) NXP

46 / 69 page

P89LPC952_954_4

Product data sheet

Rev. 04 — 24 July 2008

46 of 69

NXP Semiconductors

P89LPC952/954

8-bit microcontroller with 10-bit ADC

7.26.9 Power-on reset code execution

The P89LPC952/954 contains two special ﬂash elements: the Boot Vector and the Boot

Status bit. Following reset, the P89LPC952/954 examines the contents of the Boot Status

bit. If the Boot Status bit 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 Boot Status bit is set

to a value other than zero, the contents of the Boot Vector are used as the high byte of the

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

Table 9 shows the factory default Boot Vector setting for these devices. A factory-provided

bootloader is pre-programmed into the address space indicated and uses the indicated

bootloader entry point to perform ISP functions. This code can be erased by the user.

Users who wish to use this loader should take precautions to avoid erasing the

1 kB sector that contains this bootloader. Instead, the page erase function can be

used to erase the ﬁrst eight 64-byte pages located in this sector. A custom

bootloader can be written with the Boot Vector set to the custom bootloader, if desired.

7.26.10 Hardware activation of the bootloader

The bootloader can also be executed by forcing the device into ISP mode during a

power-on sequence (see the P89LPC952/954

User’s Manual for speciﬁc information).

This has the same effect as having a non-zero status byte. This allows an application to

be built that will normally execute user code but can be manually forced into ISP

operation. If the factory default setting for the boot vector (1FH/3FH) is changed, it will no

longer point to the factory pre-programmed ISP bootloader code. 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.

7.27 User conﬁguration bytes

Some user-conﬁgurable features of the P89LPC952/954 must be deﬁned at power-up and

therefore cannot be set by the program after start of execution. These features are

conﬁgured through the use of the ﬂash byte UCFG1. Please see the P89LPC952/954

User’s Manual for additional details.

7.28 User sector security bytes

There are eight/sixteen User Sector Security Bytes on the P89LPC952/954. Each byte

corresponds to one sector. Please see the P89LPC952/954

User’s Manual for additional

details.

Table 9.

Default boot vector values and ISP entry points

Device

Default

boot vector

Default

bootloader

entry point

Default bootloader

code range

1 kB sector

range

P89LPC952

1FH

1F00H

1E00H to 1FFFH

1C00H to 1FFFH

P89LPC954

3FH

3F00H

3E00H to 3FFFH

3C00H to 3FFFH

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