at89c5131a ATMEL Corporation, at89c5131a Datasheet - Page 5

• Manufacturer Part Number: at89c5131a
• Description: Usb Microcontrollers
• Manufacturer: ATMEL Corporation

In-System
Programming
Boot Process
High Pin Count Hardware
Conditions
Low Pin Count Hardware
Conditions
4287C–USB–11/04
ISP allows the user to program or reprogram a microcontroller’s on-chip Flash memory
through the USB bus without removing it from the system and without the need of a pre-
programmed application.
This section describes how to start the USB bootloader and the higher level protocol
over the USB.
The bootloader can be activated in two ways:
•
•
Figure 2 and Figure 3 describe the boot process flows for low pin count and high pin
count products.
The Hardware conditions (EA = 1, PSEN = 0) during the RESET rising edge force the
on-chip bootloader execution. In this way the bootloader can be carried out regardless
of the user Flash memory content.
As PSEN is an output port in normal operating mode (running user application or boot-
loader code) after reset, it is recommended to release PSEN after rising edge of reset
signal. The hardware conditions are sampled at reset signal rising edge, thus they can
be released at any time when reset input is high.
The Hardware Condition forces the bootloader execution from reset.
The default factory Hardware Condition is assigned to port P1.
•
In order to offer the best flexibility, the user can define its own Hardware Condition on
one of the following Ports:
•
•
•
The Hardware Condition configuration are stored in three bytes called P1_CF, P3_CF,
P4_CF.
These bytes can be modified by the user through a set of API or through an ISP
command.
There is a priority between P1_CF, P3_CF and P4_CF (see Figure 3 on page 8).
Note:
Hardware conditions
Regular boot process
P1 must be equal to FEh
Port1
Port3
Port4 (only bit0 and bit1)
The BLJB must be at 0 (programmed) to be able to restart the bootloader.
If the BLJB is equal to 1 (unprogrammed) only the hardware parallel programmer can
change this bit (see AT89C5131A datasheet for more details).
AT89C5131A USB Bootloader
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