AT89C51SND1_06 ATMEL [ATMEL Corporation], AT89C51SND1_06 Datasheet - Page 6

• Manufacturer Part Number: AT89C51SND1_06
• Description: USB Microcontrollers
• Manufacturer: ATMEL [ATMEL Corporation]

In-System
Programming
Bootloader
Execution
Software Boot
Mapping
Hardware Condition
Boot Mapping
Programmed
Condition Boot
Mapping
6
AT89C51SND1
The ISP allows the user to program or reprogram the microcontroller’s on-chip Flash memory
through the serial line without removing it from the system and without the need of a pre-pro-
grammed application.
This section describes how to start the USB bootloader and the higher level protocol.
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 F000h to FFFFh. The
boot memory is enabled by setting the ENBOOT bit in AUXR1 (see
set this bit are detailed below.
The software way to set ENBOOT consists in writing to AUXR1 from the user’s software. 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 2, 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 (see
As shown in Figure 2, 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 exe-
cute the bootloader software.
Table
4). The three ways to
4254C–MP3–03/06
Table
5).