Requirements

• PIC micro programmer for bootloader programming.
• PC with Windows 98/NT-SP4/2K/XP for downloader.
• One RS232 serial port available on PC.
• One female-to-male DB9 cable for serial communications.
• Application's circuit board for PIC micro updates/downloads.

Once the bootloader has been programmed into the PIC micro using any PIC programmer, the downloader can subsequently be used to download new code (HEX files) to the PIC micro.

NOTE: If a user's code has been programmed and an update needs to be downloaded, the PIC micro has to be reset in order for the bootloader to run again. This usually means the user has to push a reset button on the PIC micro board or remove and re-apply power. In certain applications this procedure is not an option. in order to avoid such procedure the downloader sends a command byte to the PIC micro which interprets it as a "reboot command" causing the bootloader to run again and therefore avoiding the need of a manual reset. The byte sent by the downloader is binary one (not the ASCII of the number one). The user should include code to recognize this "reboot command" in the PIC micro if this feature is required.

Downloader

Simply download and save the CD2m.EXE (downloader) to your computer. There is no installation program since it's a standalone application which requires no additional support files.

How to use

1. Simply select the HEX file to download using the Browse button.

2. Select the Commport your computer will use for the download.

3. Select the Baudrate depending on the PIC micro clock speed (see below on the Bootloader section).

4. Select Start and look for messages on the window title bar. If download failed try again.

Bootloader

There is a specific bootloader for each PIC micro, 16F873, 16F873A, 16F876 or 16F876A. The frequency of the clock is also a factor. The baudrate has been selected to the maximum possible permitted by the clock frequency for faster downloads.

16F870

• PIC16F870 @ 4MHz @ 19200 bps
• PIC16F870 @ 10MHz @ 57600 bps

16F873 (compatible with 16F874 too)

• PIC16F873 @ 4MHz @ 19200 bps
• PIC16F873A @ 4MHz @ 19200 bps
• PIC16F873 @ 10MHz @ 57600 bps
• PIC16F873A @ 10MHz @ 57600 bps
• PIC16F873 @ 20 MHz @ 115200 bps

16F876 (compatible with 16F877 too)

• PIC16F876 @ 4MHz @ 19200 bps
• PIC16F876A @ 4MHz @ 19200 bps
• PIC16F876 @ 10MHz @ 57600 bps
• PIC16F876A @ 10MHz @ 57600 bps
• PIC16F876 @ 20 MHz @ 115200 bps
• PIC16F876A @ 20 MHz @ 115200 bps

Custom frequencies (such as 9.8342Mhz @ 9600bps) can be ordered online for $US49.

Here are the programming PIC micro settings for the bootloader using Microchip's MPLAB and Pro Mate II:

Setting	Value
Oscillator	Depends on the application. (for resonator frequencies higher than 4MHz use HS).
Watchdog Timer	Off (if On, must add support in your code)
Power Up Timer	On
Code Protect	Off
Brown Out Detect	On
Low Voltage Program	Disabled
Data EE Protect	Off
Flash Program Write	Enabled/Off (16F87xA)
Background Debug	Disabled

NOTE: If an universal programmer is used the same settings should apply. It may only be that are named slightly differently.

Troubleshooting

1. This bootloader is known to be compatible with .hex files produced by the Hi-Tech C compiler. It is not tested with anything else.
2. This bootloader will not work with the 16F872 - it has no UART.
3. The bootloader will only work with .hex files that have a long jump as the first 4 words, precisely the same as the following:
   
   ORG 0x0000 ;reset vector
   clrf 0x3 ;zero status
   movlw 0x00 ;high byte of long jump
   movwf 0xA ;zero PCLATH
   goto start ;ie: if 'start' offset=0xFD, execute long jump to 0x00FD
   ;bootloader executes these 4 instructions to jump from top of memory, back to program entry point
   ;reset vector is at ORG 0x0004, from here on.
   
4. The .hex file must not use the top 256 words in memory, as these are occupied by the bootloader. For the 16F876, this is locations 0x1F00 to 0x1FFF. For instructions on how to reserve the top 256 words in memory, refer to http://www.microchipc.com/PIC16bootload/.
   
5. Double check the that the serial port is communicating correctly with the PIC micro. For example, for a 16F87xx @ 20Mhz, program "_19200 - test_serial_link_19200baud_20Mhz.hex" into the micro. Set up HyperTerminal to communicate at 19200bps, N,8,1, No flow control, and check to see if the word [alive] is sent continuously. If the serial communications with the micro are working properly, then the bootloader should work properly too.
   
6. A MAX232 or similar is required to level shift the TTL logic levels (0V / +5V) of the PIC micro to the RS232 voltage levels (+13V / -13V). See http://www.microchipc.com/PIC16bootload/ for more information.

Tribute

Many thanks to carlos.buelna@delphiauto.com for this excellent piece of coding. Additional troubleshooting and 'A' rev hex files added by shane@microchipc.com.