P89LPC938 NXP Semiconductors, P89LPC938 Datasheet - Page 45

• Manufacturer Part Number: P89LPC938
• Description: The P89LPC938 is a single-chip microcontroller, available in low cost packages, based ona high performance processor architecture that executes instructions in two to four clocks,six times the rate of standard 80C51 devices
• Manufacturer: NXP Semiconductors

Philips Semiconductors
9397 750 14051
Product data sheet
7.28.10 Hardware activation of the boot loader
7.28.8 ISP
7.28.9 Power-on reset code execution
In addition, IAP operations can be accomplished through the use of four SFRs consisting
of a control/status register, a data register, and two address registers. Additional details
may be found in the P89LPC938 User’s Manual .
In-System Programming is performed without removing the microcontroller from the
system. The In-System Programming facility consists of a series of internal hardware
resources coupled with internal firmware to facilitate remote programming of the
P89LPC938 through the serial port. This firmware is provided by Philips and embedded
within each P89LPC938 device. The Philips In-System Programming facility has made
in-system programming in an embedded application possible with a minimum of additional
expense in components and circuit board area. The ISP function uses five pins (V
TXD, RXD, and RST). Only a small connector needs to be available to interface your
application to an external circuit in order to use this feature.
The P89LPC938 contains two special Flash elements: the Boot Vector and the Boot
Status Bit. Following reset, the P89LPC938 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 is used as the high byte of the
execution address and the low byte is set to 00H.
Table 8
boot loader is pre-programmed into the address space indicated and uses the indicated
boot loader 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 boot loader. Instead, the page erase function can be
used to erase the first eight 64-byte pages located in this sector. A custom boot
loader can be written with the Boot Vector set to the custom boot loader, if desired.
Table 8:
The boot loader can also be executed by forcing the device into ISP mode during a
power-on sequence (see the P89LPC938 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) is changed, it will no longer point to the
factory pre-programmed ISP boot loader 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.
Device
P89LPC938
shows the factory default Boot Vector setting for this device. A factory-provided
Default Boot Vector values and ISP entry points
Default
Boot Vector
1FH
Rev. 01 — 25 February 2005
Default
boot loader
entry point
1F00H
8-bit microcontroller with 10-bit A/D converter
Default boot loader
code range
1E00H to 1FFFH
© Koninklijke Philips Electronics N.V. 2005. All rights reserved.
P89LPC938
1 kB sector
range
1C00H to 1FFFH
DD
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, V
SS
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