There is a plethora of information scattered on the web about this chip, but no one place provides a complete set of instructions to get you started. This project is my attempt to provide just that. So, first of all, you need a 80C52 or compatible microcontroller. Once you have the controller, you need a board to stick it in. Click here to see the schematics.
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This will install the application on your computer and add the appropriate icons to your "Programs" menu.
You may then launch the program normally. To Write Firmware to the Microcontroller: In order to write firmware to the microcontroller, first select the HEX file you wish to download by pressing the "file" button to the right of the "File to Program" prompt. You will be allowed to select a HEX file which will be loaded into memory. A progress window will be displayed as the file is transferred to the microcontroller.
To Read Firmware from the Microcontroller: You may read the contents of a microcontroller by pressing the "Read" button. This will download the program memory from the microcontroller to the PC. When the download is complete you will be prompted to enter a name for the HEX file that you wish to write the data to. Note that you will not be able to download firmware if the microcontroller has a security "lock bit" set to prohibit such downloading. To Erase the Microcontroller: You may erase the microcontroller by pressing the "Erase" button.
You may cancel this verification process at any time without affecting the erase process which is completed almost immediately. You may also toggle the "Quick Program Mode. If this option is not selected then the remaining 6k will be filled with FFh data.
The The D1 pin of the parallel port drives the RST pin of the microcontroller. This allows VisISP to put the microcontroller into reset mode. This is necessary because ISP occurs with reset driven high. When this line is low, the other three input lines should not be connected to their respective connections on the microcontroller.
Note that a pull-down resistor between the parallel port and the 74HC may be necessary so that ISP is disabled when no parallel cable is connected to the ISP circuit. Data sent from the microcontroller to VisISP is sent on this line. Note that a termination resistor of approximately Ohms is recommended between the 74HC latch and the parallel port pin. As many pins between 18 and 25 of the parallel port should be connected to ground on the microcontroller circuit.
While a single ground line may work, connecting additional ground lines may decrease problems due to crosstalk between the data lines. This is especially true if the parallel cable is a flat ribbon-cable.
This is the designed that is implemented in the Click on the schematic for a larger version. That software works fine in Linux and probably works fine in Windows; however, the install process was not particularly friendly for Windows NT and Windows XP due to additional software that needed to be installed in order to access the parallel port which is protected in those operating systems. VisISP solves both of these problems by providing a single easy-to-install application that will work on any modern Windows operating system.
The AT89S code was developed from scratch with some limited technical support from Atmel. The software also includes code based on the parallel port code from Logix4U. This software is free and may be distributed without restriction.
The source code is not currently available but will probably be made available in the future. The only the source code is not being made available at this time is because the code is not as presentable or as easy-to-follow as it should be and will probably confuse the curious developer rather than help him.
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