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AT89C5131A Datasheet(PDF) 5 Page - ATMEL Corporation |
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AT89C5131A Datasheet(HTML) 5 Page - ATMEL Corporation |
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5 / 33 page  5 AT89C5131A USB Bootloader 4287C–USB–11/04 In-System Programming 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. Boot Process The bootloader can be activated in two ways: • Hardware conditions • Regular boot process Figure 2 and Figure 3 describe the boot process flows for low pin count and high pin count products. High Pin Count Hardware Conditions 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. Low Pin Count Hardware Conditions The Hardware Condition forces the bootloader execution from reset. The default factory Hardware Condition is assigned to port P1. • P1 must be equal to FEh In order to offer the best flexibility, the user can define its own Hardware Condition on one of the following Ports: •Port1 •Port3 • Port4 (only bit0 and bit1) 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: 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). |
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