In Circuit Programming
Colin Mitchell
Colin Mitchell
May 05, 2010
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Table Of Contents

Page of Contents

  • Chapter 1
  • Chapter 2
  • Chapter 3

Chapter 4


The PIC12F629 comes in:

PIC12f629 small
PIC12f629 small

8-pin (through hole) 8/PDIP PIC12F629I/P

8PinSMD small
8 Pin SMD small

8-pin SMD (surface mount) PIC12F629-I/SN 8/SOIC package

Buy: ICSP-1t PCB and parts for through-hole chip. Approx $7.00
or ICSP-1s PCB and parts for surface-mount chip. Approx $7.00
To place an order, click: [ICSP PC boards](mailto:colin@elechelp.com?Subject=Buying ICSP PC boards&Body=Please e-mail the cost of sending In-Circuit Serial Programming PCB ICSP-1t or ICSP-1s kit by air mail to my country:****___**** and send details of how I can pay for it. My name is:____)
Buy: PICkit-2 serial programmer and interface lead. Approx $50.00
(see below for answers to PICkit-2 questions). The PICkit-2 comes with 2 CDs containing the programming software for the USB port on your computer.
See MicroChip website for PICkit-2 forum

This the place to start if you want to design a small project using a PIC12F629 and program it via “In-Circuit Serial Programming.”
We have designed PC boards for both the through-hole version of the chip and the surface-mount version. The boards contain 2 LEDs to test a simple program and extra lands for additional components.

Some PIC12F629 Projects:


Choose one of the projects from Pick A PIC Project page. Build it and use the PICkit-2 serial programmer and interface lead to program the chip or alter the program.
You will need the Data Sheet, Instruction-Set, template and Library of Routines to help you with writing or modifying a program.


Design your own project on the ICSP-1s board.

If you have programmed a microcontroller before or are new to programming, the latest “trick in the book” is ISP.
This article will help you connect PICkit-2 programmer to a fully developed project that has 5 pins. These pins connect to the PIC chip and also accept a 6-pin to 5-pin connector (available from Talking Electronics).

The following photo shows the top and bottom of the connector designed by Talking Electronics to interface between the programmer(PICkit2) and the PC board:

6pin 5pinConnector 1
6 pin 5 pin Connector 1

6pin 5pinConnector 2
6 pin 5 pin Connector 2

The 6-pin to 5-pin connector

Imagine developing a surface-mount project and being able to update the program while the chip is soldered to the board.
Obviously this is essential for a surface mount design as it is totally impractical to desolder the chip to change the program.
In this project we show how to design a PC board to contain the 5-pin ICSP (In-Circuit Serial Programming port).
We have also written a number of projects using a surface-mount microcontroller.
These project are all available as a kit with a pre-programmed micro, but if you want to modify the program, you will need a programmer and an interface cable.
Also, if you want to design your own surface-mount project, this article will get you started.
This article help you with the simplest 8-pin surface-mount PIC microcontroller.
It is a PIC12F629 8-pin surface mount device with the code number PIC12F629-I/SN 8-pin SOIC (Small Outline Plastic Packages) 150mil.
The package is identified by: SOIC-8. The surface mount version of a PIC12F629 is identified by “I/SN.” The 8-pin dial in line version is: PIC12F629I/P

Pin 1 identification of an 8-pin surface mount chip PIC12F629I/SN

This chip has a small memory, but don’t let that put you off. We will be producing projects equal to up to 10 of the old-style chips and some of our projects will even appear to be “intelligent.”

When writing a program understood by the microcontroller, the term is called “Machine Code.” But since a chip only understands 0’s and 1’s, it is very difficult for humans to remember an instruction with a number such as 10110101101100. To make it easier, manufacturers have created instructions that look like the words of the instruction. These words are called mnemonics and the chip we are using has only 33 instructions. A typical instruction is: Increment a file and skip the next instruction if the file is zero.
The mnemonic is: INCFSZ - each letter in the instruction corresponds to a word in the instruction. All the other instructions are the same, and we can add more information to the previous instruction by identifying the file-number and if the result of the increment is placed in the same file or sent to another file called the “working file.”
All this can be placed on one line of your program thus: INCFSZ f,1.
The chip has 1,024 locations for instructions.
Some instructions carry out a simple task such as setting or clearing a bit: BSF file,bit BCF file,bit while others can swap the contents of the working register (W) with a file.
SWAPF file,0 SWAPF file,1 where “0” represents the working register (W) and “1” represents the same file named in the instruction.
See the PIC12F629 Instruction Set.

Although the chip looks small and has only 8 pins, two are for connecting to the power and 6 lines are in/out. The chip can control 5 devices and one line is input only (pin 4). The 5 output lines can be changed to input at any time during the running of the program and this gives you great flexibility.

The functions for each pin:

Note: Pin 4 is INPUT ONLY

These chips are not a “computer on wheels” but they will get you started into the world of programming and thinking of ideas that could lead you down the path of invention.
To give you three examples, an inventor in our club designed a letter bomb detector from a gold detector and went on to sell nearly 1,000 units and realise nearly $3.5M in sales. 7 people have been saved from unknown explosive devices and he sells his invention throughout the word. If he had put the requirements into a chip as simple as the one we are promoting, his circuit would be 75% smaller.
Another designer built a telephone number storage device for 20 numbers. He used 16 chips. Our chip would carry out the task without any other components.
Another designer produced a medical timing device for patients and sold it to a drug company. His chip was added to a speech chip and everything was produced as a “COB.” (Chip On Board). He had 200,000 made. It had 20 seconds of speech, controlled by turning the cap of the bottle. It explained when to take a tablet.
These are just some of the possibilities.

The microcontroller can do things like turning on an output (making it go HIGH) and keeping it HIGH for any length of time. By making an output go high/low/high/low, the result is a tone.
An output has sufficient ability to drive a LED (25mA) and this gives us the ability to drive 5 LEDs at the same time.
The other line can be used as an input.
A LED will turn on and off very fast and when they are moved through the air and activated correctly, the result is writing. That’s why we call the project SKYWRITER.


On your desktop you will need 4 icons:

Icons 4
Icons 4

At the beginning you can create 3 folders and name them as above.
Notepad2 will be inside PICkit-2 Files folder.

Set-up a folder called PICkit-2 Files (or PICkit-3) in which you will place the programs for all your projects.
You will need:
Notepad++ or VS Code in the same folder so you can take a .asm file from one of the projects we have produced and use it to write your own program.

Your first file will be: sample.asm When you select sample.asm, it will use Notepad2, so have notepad2 in the PICkit-2 Files folder so your computer can find it.

Set up another folder with MPASM

In the MPASM folder you will have MPASM and you will select

  • Radix default

  • Warning Level Default

  • Hex Output Default

  • General Files: tick Error File tick List File

  • Select 12F629 from Processor “drop down box”

  • Macro Expansion default

  • Tab size 8

  • tick save settings on exit

  • and a third folder with PICkit2v2.exe and ”[.inc files](//TODO FIXME inc%20files)”

  • The Programming routine comes inside the Programmer.zip file with PICkit2DeviceFile.dat

  • Unzip Programmer.zip to produce PICkit2v2.exe and PICkit2DeviceFile.dat

  • From this “Programmer” folder, you will hyperlink to PICkit2v2.exe


The first thing you must remember is this: 3 pins are needed for IN CIRCUIT PROGRAMMING. These are pins 4, 6 and 7. Pin 4 is an input-only pin. Pins 6 and 7 are GP1 and GP0. If you need to connect devices to pins 4, 6 and 7, the programmer needs to drive the pins HIGH and LOW during programming..
It is capable of delivering more than 25mA (in other words it has a low output impedance of about 40 ohms) but do not connect a capacitor or electrolytic to these pins as the electro will prevent programming. Pin 4 needs to go HIGH (about 14v) during programming, so any device sending a signal to the pin needs to accept 14v, see below:

The following diagram shows a SURFACE MOUNT PC Board with a PIC12F629 chip and IN-CIRCUIT PROGRAMMING socket made from 5 tinned copper wires.



The photo below shows fine enamelled wire (0.2mm) connecting the programming pins to the surface-mount chip and MicroChip PICkit-2 programmer:

8 Pin SM top

pickit2 large
pickit 2 large

The photo identifies each of the pins for the surface-mount chip:

8PinSMtop 2
8 Pin SM top 2

The photo below shows fine enamelled wire (0.2mm) connecting the programming pins to an 8-pin IC socket:

8 Pin Top

The names of each of the pins for the 8-pin IC socket:

8 Pi nSM ISO

The connector and surface-mount chip

8 Pin ISO

The connector and 8-pin IC socket

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1. What is a PICkit 2?

The PICkit 2 is a USB in-circuit prototype programmer manufactured (and sold) by Microchip.

The PICkit 2 contains an 18F2550 chip. This chip can update its code (write to its own FLASH memory). The PICkit 2 contains a bootloader that makes this possible. You can use this feature to update the firmware of your PICkit 2.

With the latest version of MPLAB (7.41) it should be possible to use the PICkit 2 as an ICD (in-circuit debugger, like ICD1 or ICD2), but only with the PIC16F917. So far I have not been successful with this.

2. What is ‘in-circuit’?

The PICkit 2 is an in-circuit programmer, which means that it does not have a ZIF or similar socket to plug the target chip (the chip to be programmed) in. Instead it has a connector for a 6-pin, which you must connect to the target chip. With some care this enables you to program the target chip without removing it from its circuit.

3. What is ‘prototype’?

To be really sure that a PIC is correctly and long-term reliably programmed it must be verified (by reading the code back and comparing it to the original) at the low and high extremes of the power supply voltage that it will be used with. Microchip calls a programmer that can do this a ‘production’ programmer. A programmer that does not have this capability is called a ‘prototype’ programmer, indicating that it should not be used for development only, not for production work. The PICkit2 hardware has a limited ability for varying the supply voltage for the target chip (it can only regulate down from the voltage supplied by the USB connection, and its only reference is that voltage), and the current PICkit2 software uses this ability only to reduce the supply voltage to 3.3V for chips that cannot use a higher voltage. Hence the PICkit2 is called a ‘prototype’ programmer.

4. What is a ‘bootloader’?

Generally speaking a bootloader is a (small) program, which sole purpose is to load another program (the application) into memory (and probably to start that application). In the context of FLASH microcontrollers a bootloader is a program that can write an application program to the FLASH memory of the microcontroller (it can of course write only to the part of the FLASH that is not occupied by the bootloader itself). The PICkit 2 contains a bootloader that will takes control when the PICkit 2 is powered. When the bootloader does not find an application program already in FLASH, or it finds the PICkit 2 button pressed, it will remain in control. Otherwise it will pass control to the application program (the PICkit 2 firmware itself).

When the bootloader is in control it will blink the Busy LED.

5. How can I download/update the PICkit2 firmware’?

The PICkit 2 XP program supplied by Microchip has a menu entry ‘Download PICkit 2 OS firmware’ under ‘tools’. This will instruct the PICkit 2 application to pass control to the firmware and let you pick a .hex file to be downloaded.

If your PICkit 2 contains the bootloader but no application the bootloader will remain in control (the Busy LED will blink). When you start the PICkit PC program it will take some time during which nothing seems to happen (don’t panic). Then a window appears that allows you to choose the application .hex file to download. This also takes some time. Then the normal PICkit 2 application window will appear, but it shows a nonsense message about a strange firmware version. You can ignore that message.

6. The software in my PICkit 2 seems to be corrupt, what can I do?

If an application is present in the PICkit 2 but it is corrupted (or it is not the PICkit 2 firmware) you can not use the normal software update method. Instead you must plug the PICkit 2 in (USB cable) while pressing the button. This forces the bootloader to invalidate the application and take control. Now you can proceed as stated in the previous answer.

7. What is the purpose of that button?

The PICkit2 has a small black button right above the power LED. When it is pressed while the USB connection is made the bootloader will claim control instead of activating the PICkit2 firmware. This can be used to update a damaged firmware.

The PICkit2 hardware has two 24LC512 EEPROMs. With the current firmware these EEPROM are not used. With appropriate firmware (which to my knowledge does not yet exist) the PICkit2 could be used as a stand-alone programmer: use a PC to load the software update into the EEPROMs, drive to the device you want to update, plug the PICkit2 in, press the button, and the new software is programmed into the device. The device must provide power to the PICkit2, and the target PIC must be one that can be programmed with a Vdd-before-Vpp sequence.

8. Which USB driver do I need?

You don’t need a special USB driver, the PICkit 2 uses the HID (Human Interface Device) driver that is part of Windows XP.

9. I get ‘USB device not recognised’, what should I do?

This problem is often reported by PICkit 2 users. I don’t have a definitive solution, but some thing seem to help:

  • disconnect the PICkit 2 from the target circuit before you connect the USB cable
  • plug the USB connector in slowly (this increases the time between the power contacts connecting and the data contacts connecting)
  • when you get the error, disconnect, wait a few seconds, and reconnect.
  • contrary to the above, some people have reported that you must wait a long time (>30 seconds?) before you attempt to reconnect. I suspect that this is a cure for a different problem.
  • if the PICkit 2 is connected to a HUB, disconnect the HUB from the PC and reconnect (I still saw the ‘USB device not recognised’ error but the device did work!)
  • (a bit experimental) during experiments with a PICkit 2 clone I am designing I noticed that the ‘USB device not recognised’ was produced by the PICkit 2 application, never by the bootloader, and also never immediately after the application was downloaded and started by the bootloader. The USB part of the application and bootloader work a bit different, so I reasoned that maybe the bootloader does a better job on the USB initialisation. But the original bootloader does not initialise the USB, except when no application is present, or the button is pressed. So I modified the bootloader to *always* initialise the USB, wait a second, shut down the USB, and then start the application (if present). You can hear this: when you plug it in you hear a USB attach, USB detach, and a final USB attach. So far I never got the ‘USB device not recognised’ with this modified bootloader. To use this bootloader you will have to re-program your PICkit 2. When you open it you will notice a strip of 6 pads at the edge of the PCB. These pads can be used to (re) program the 18F2550 in the PICkit 2 with … a PICkit


If you want the PICkit-2 serial programmer to be connected constantly to a chip during the development of a program, it has a number of limitations when programming a chip that is connected to low-impedance devices.
When a chip is being programmed “in circuit,” some of the devices being driven by the chip are activated during the programming operation.
Even though each output is only capable of delivering 25mA, the combined current from 4 outputs on the Random Number project was sufficient to create a problem. The current taken by the circuit was in excess of the current-capability of the components in the PICkit-2 and the output voltage dropped excessively - preventing the chip being programmed.
The solution was to drive the circuit from the supply powering the circuit and have a switching transistor to do this when the programmer was in program-mode. This removed the excess current from the programmer.


Buy: ICSP-1t (In Circuit Programming board for through-hole chip plus IC socket and plug and wire and fine solder) Approx $7.00
or ICSP-1s (In Circuit Programming board for surface-mount chip and plug, wire and fine solder) Approx $7.00
To place an order, click: [ICSP PC boards](mailto:colin@elechelp.com?Subject=Buying ICSP PC boards&Body=Please e-mail the cost of sending In-Circuit Serial Programming PCB ICSP-1t or ICSP-1s kit by air mail to my country:****___**** and send details of how I can pay for it. My name is:____)
Buy: PICkit-2 serial programmer and interface lead. Approx $40.00

Place the chip on the board and all the components from the kit. You will need a 5v supply made from 4 AA or AAA cells. Connect the interface lead to the board and PICKit-2. Connect the PICkit-2 to the USB port on your computer and insert the MPLAB IDE CD that comes with the programmer. Load MPLAB onto your computer.

Now go to: Start HERE with PIC12F629 to learn how to write a simple program for the chip.
You will need Notepad++ or VS Code to load PIC12F629 template. You can then modify the template to create your own program.


Colin Mitchell

Colin Mitchell



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