AT89C5131A-L Atmel Corporation, AT89C5131A-L Datasheet - Page 5
Manufacturer Part Number
Specifications of AT89C5131A-L
Max. Operating Frequency
Max I/o Pins
Self Program Memory
Operating Voltage (vcc)
3.0 to 3.6
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
This section describes how to start the USB bootloader and the higher level protocol over the
The bootloader can be activated in two ways:
Regular boot process
Figure 3 and Figure 4 describe the boot process flows for low pin count and high pin count
High Pin Count
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. It is recommended to pull the PSEN pin down to ground though a 1K resistor to
prevent the PSEN pin from being damaged (see Figure 2 below).
Figure 2. ISP Hardware conditions
As PSEN is an output port in normal operating mode (running user application or bootloader
code) after reset, it is recommended to release PSEN after rising edge of reset signal. The hard-
ware conditions are sampled at reset signal rising edge, thus they can be released at any time
when reset input is high.
Low Pin Count
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
AT89C5131A USB Bootloader