Bootloader Tool Known as Zero Pin Loader

Overview

The zero pin loader is a bootloader for the PICmicro 18F series in order to avoid the use of I/O pins by exploiting the /MCLR pin as the solitary interface between the PICmicro and the host PC.

Explanation

The main part of the circuit is the PIC16F877 microcontroller that is capable of writing to their own code memory. There are 6 components used as the interface between the target and the PC serial port. The standard /MCLR pull-up resistor is one of the components with two optional. Other types of connection include putting the interface circuit in a common DB9 shell and with a DIP clip for the connection to the target.

For the device to run on Windows and Linux, the host PC is written in Python, making it easily ported to other operating systems. 70 seconds is the clock download time for a full 18F452 that contains 32k instructions less the 384 for the bootloader.

The circuit will not interfere with the normal operation of the target circuit when no host is connected. The correct serial port is made sure using a series resistor and a LED, although not necessary.