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Loader420: DS89C420 Serial Loading Utility

Loader420 is a utility that allows an embedded system designer to quickly and easily communicate with the DS89C420 High-Performance Microcontroller through the serial port of a PC. The program acts as a high-featured front-end to the bootstrap loader built into the DS89C420, simplifying the task of uploading and downloading code while still in the application. Minimal external hardware interfaces the PC to the DS89C420 and activates the bootstrap loader.

The following features are supported:

•	Load Intel hex file to target device

•	Verify contents of device memory against Intel hex file

•	Erase target device

•	Dump specified range of device memory to screen (Intel hex record format)

•	Display specified range of device memory to screen (memory+ASCII format)

•	Calculate CRC over specified memory range

•	Configure/read SFRs related to Flash programming and I/O ports

•	Control external loading hardware via COM port DTR signal

System Requirements

Windows 95/98/2000/ME/NT or more recent operating system

Available COM port (COM1/COM2/COM3/COM4)

Quick start

1. Connect the DS89C420 to the PC via an external hardware interface

2. Select the COM port and baud rate

Ports -> Select Port Settings

3. Open the COM port by pressing the OPEN button at the bottom of the window

4. Activate the DTR signal (which invokes the DS89C420 loader) by pressing the Loader button at the bottom of the window. The DS89C420 should return its sign-on banner
DS89C420 LOADER VERSION 1.0  COPYRIGHT (C) 2000 DALLAS SEMICONDUCTOR

>

(Note that the version number may differ slightly depending on the device revision)

5. Select the Intel hex file (.hex) to be loaded

File -> Load File

The application will show percent completion as it loads and respond with "Done loading file" when complete.

6. If desired, you can verify the load by clicking the Verify button on the memory access bar and selecting the same file you loaded.

On subsequent loads of the same file, the Reload button is a shortcut.

The interface screen

The application window is divided into 4 sections. The first, at the top, is the memory access bar, used to upload and download files and examine memory contents. The range Begin/End values apply to the Dump, Display, and CRC functions. Next is the SFR access bar, allowing the user to modify or examine the contents of certain SFRs that can affect the device during program loading. Next is the main display window, showing the progress of various Loader420 operations. At the bottom is the interface control bar, which controls Loader420 access to the PC COM port and sets/clears the COM port DTR signal used to control external hardware.

Interfacing the PC to the DS89C420

The external hardware interface to the DS89C420 is quite simple. To activate the internal bootstrap loader of the DS89C420, the RST pin must be pulled high and the EA\ and PSEN\ pins must be pulled low. Communication to the bootstrap loader is performed via serial port 0. Loader420 is designed to use the COM port DTR signal (active low) to activate/deactivate the bootstrap loader, which greatly simplifies the loading process. The following illustration shows one possible hardware configuration that will interface the DS89C420 to the PC. This configuration allows in-application programming, as it is completely transparent when the DTR signal is not active.