at89c51snd1 ATMEL Corporation, at89c51snd1 Datasheet - Page 6

• Manufacturer Part Number: at89c51snd1
• Description: Mp3 Microcontrollers
• Manufacturer: ATMEL Corporation

In-System
Programming
Bootloader Execution
Software Boot Mapping
Hardware Condition Boot
Mapping
Programmed Condition Boot
Mapping
6
AT89C51SND1 UART Bootloader
The ISP allows the user to program or reprogram a microcontroller’s on-chip Flash
memory through the serial line without removing it from the system and without the need
of a pre-programmed application.
This section describes how to start the UART bootloader and the higher level protocol
over the serial line.
As internal C51 code space is limited to 64K Bytes, some mechanisms are implemented
to allow boot memory to be mapped in the code space for execution at addresses from
F000h to FFFFh. The boot memory is enabled by setting the ENBOOT bit in AUXR1.
The three ways to set this bit are detailed below.
The software way to set ENBOOT consists in writing to AUXR1 from the user’s soft-
ware. This enables bootloader or API routines execution.
The hardware condition is based on the ISP# pin. When driving this pin to low level, the
chip reset sets ENBOOT and forces the reset vector to F000h instead of 0000h in order
to execute the bootloader software.
As shown in Figure 3, the hardware condition always allows In-System recovery when
user’s memory has been corrupted.
The programmed condition is based on the Bootloader Jump Bit (BLJB) in HSB. As
shown in Figure 3, this bit is programmed (by hardware or software programming
mode), the chip reset set ENBOOT and forces the reset vector to F000h instead of
0000h, in order to execute the bootloader software.
4241B–MP3–07/04