PIC Programmers, In Circuit Programming and BootLoaders

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In the PIC world programming may mean either writing the program by a human being or writing the hex file from the compiled ( assembled ) program into the PIC chip. This page concenrns the latter.

Overview

There are several different methods of programming each with its own advantages and disadvantages. Right now I like serial bootloading the best, but it may not be the best for everyone. The following chart summarizes the methods, they are then discussed in more detail later.

Method	What	Details
Hardware Programmer	The PIC is placed in the programmer and the programmer workds with a PC ( typically ) to move the program to the PIC.	All chips can be used with Hardware Programmer, but different chips may require different programmers.
In Circuit Programming	The PIC is installed in the target board, and then never moved again. The programmer is plugged into a "programming connector" on the target board each time you want to reprogram the PIC.	Not all chips can be used with In Circuit Programming.Template:Fact
Serial Bootloaders	In this method a small program ( the Serial Bootloader ) is hidden away in the PIC memory and upon reset the PIC would check its serial connection and if connected to a Bootloader utility on the connection a new program is loaded into the PIC, and then the downloaded program begins. If the Bootloader utility is not connected the current PIC program is run. The serial connection can be of any type, RS232 or USB for example.	Requires initial programing with a Hardware Programmer, and the serial connection. The PC runs the Bootloader utility. Not all chips can be used with Serial Bootloaders.

Hardware Programmer

Advantages

• There is some programmer for every chip, and many support a very wide range of chips including one time programmable chips.

Disadvantages

• Need to remove PIC from its circuit and put in the programmer's socket.
• Extra cost for the programmer.

for links to programmers see: PIC Links search for "Programmer"

In Circuit Programming

Advantages

• Do not need to remove chip from the PIC circuit.

Cypress says "ISSP ... stands for In-System-Serial-Programming. We recommend that all PCBs be designed to support ISSP. During the prototyping phase it is very convenient for the hardware of software engineer to be able to re-program a PSoC device on the prototype board. This is much easier than removing the PSoC device, reprogramming it and replacing it on the PCB. This is especially true when using surface mount devices." -- Cypress "Programming a PSoC In System"

"Atmel AVR910: In-System Programming"

Disadvantages

• Not all chips support in circuit programming.

Serial Bootloaders

Advantages

• Do not need to remove chip from the PIC circuit.
• Often only requires you to shift the PC software to the Bootloader utility.
• Very quick for test, revise, retest cycles.
• No special hardware required, cheap.

Disadvantages

• Not all chips support in serial bootloaders.
• PC may not have the required serial port.
• Requires serial hardware, but your circuit may already have it.
• You may have to compile or assemble your bootloader to configure it for your needs, it may not be in the same language you would normally use.

With a Serial Bootloaders there are two software components ( in addition to the hardware serial connection ) the Bootloader utility running on the PC and the PIC bootloader on the PIC. If you program is going to use a serial interface any way ( even if just for debugging ) this can be a very nice way of programming, you do not have to move one bit of hardware to go from programming to running to programming to ....... The bootloader is a small program that is tucked away, normally in high memory, that checks at startup to see if it is connected to a PC bootloader utility. If so it dowloads a new program to the PIC, else it it runs the PIC program.

The PIC bootloader must be configured for the target chip and the configuration of the PIC, generally speaking the user program must share the configuration of the bootloader as the bootloading process does not change the configuration. Because of this bootloaders are often distributed in source code form ( usually asm ) so that you can tweak the code and assemble it for yourself. Often there will be several pre-built hex files and one of these may or may not work for you. Once you have the right bootloader you use a Hardware Programmer to write the bootloader to the PIC for hopefully the first and last time ( a badly behaved program can destroy the bootloader requiring a reload ).

In some cases you may buy a chip that already contains the bootloader -- this can save a certain amount of work.

The following is just draft:

You may be able to use a bootloader at a different baud rate than intended if the crystal is different. Both need to change by the same factor.

Name	Source	Details
Tiny Bootloader	Tiny PIC bootloader	A bunch of different PICs
Bloader and Screamer	Bloader and Screamer	from our friends at SparkFun. Supports: 16F877A (20 and 4MHz), 16F876A (20 and 4MHz), 16F873A (20 and 4MHz), and 16F88 (20/4MHz external, 8MHz internal)
PIC downloader 1.08	PIC downloader	need comment
name	[ ]	need comment

Tested tool chains for Serial Bootloaders -- if you Chip/Hardware is close this might be a good place to start.

Method	What	Details
Chip/Hardware	Tool Chain	Link
877A 20 meg crystal and clock	on PIC bootldr-16F877A-20MHz-38400bps.HEX on PC PICdownloader.exe download at 38.4 K baud	I forget
16F877A 4 meg Hz crystal and clock	on PIC: bootldr-16F877A-16MHz-38400bps.HEX on PC: PICdownloader.exe download at 9.6 K baud ( note that this is 1/4 of the intended baud because the crystal is 1/4 of the target crystal )	I forget
18F2550 20 meg Hz crystal 24 meg Hz clock	On PIC: tinybld18F2550usb _20MHz_115200.HEX On PC: TinyBootloader download at 115.2 K baud This worked fine the first time after programming the bootloader, after first bootload it would not work a second time. Doing a power off and on to reset seems to make it work time after time. More testing needed. This baud rate is high, I have changed it to 19.2K to see if it is more reliable at that speed. Again more testing needed.	Tiny PIC bootloader

Further reading

• Bootloader Development
• "Embedded Systems/Bootloaders and Bootsectors"
• "PIC Microcontroller Programmers" discusses in-circuit programmers and bootloaders