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Programming PICs: How It’s Done Many SILICON CHIP projects include a PIC microcontroller as the central component. But how do you program the PIC if you’re not buying a kit or if you want to upgrade the firmware to a later version? Here’s a step-by-step guide to doing it yourself. By MAURO GRASSI F OR MANY ELECTRONICS enthusiasts, programming the PIC micros that are now used in so many SILICON CHIP projects is something of a mystery. If you buy a kit, it usually doesn’t matter because the micro will be supplied pre-programmed. Alternatively if you’re building a project from scratch, then you’ve either got to pay someone to do it for you or learn how to do the job yourself. A similar problem arises if the PIC fails and has to be replaced or if you want to update the firmware to a later version. It’s not uncommon for the firmware to be revised after a project has been released, usually to add extra features but also sometimes to fix any bugs. Fortunately, programming PICs is straightforward although you do require a low-cost PIC programmer (more on this shortly). By following the simple steps outlined in this article, you will be able to program almost any Microchip microcontroller, including the popular 16F, 18F, dsPIC33F, PIC24F and PIC32 families. A few basics PIC microcontrollers have onboard non-volatile memory (FLASH) that stores the program code (some also have onboard EEPROM for storing persistent data). This program code is referred to as the “firmware”. The term “non-volatile” simple means that the firmware remains in memory even when the power is turned off. Programming (or reprogramming) can be done in at least two ways: (1) through “ICSP” (In Circuit Serial Programming) or (2) through “RTSP” (Run Time Self Programming). The latter option requires a “bootloader” program to be running on the target device. A bootloader is a separate program that can write a new firmware image onto a microcontroller. The firmware image is supplied to the bootloader usually via Table 1: Programming & Power Supply Connections Line Function Connect To PICKit3 Line PGD or PGED Programming Data Line Pin 4 (PGD) PGC or PGEC Programming Clock Line Pin 5 (PGC) Bar-MCLR/VPP Programming Voltage Pin 1 (bar-MCLR/VPP) VDD Device Voltage Pin 2 (VDD) VSS Device GND Pin 3 (GND) AVDD Analog Device Voltage Pin 2 (VDD) AVSS Analog Device GND Pin 3 (GND) 26  Silicon Chip a USB or serial connection, or from some other storage medium (eg, a memory card). In most cases, however, a bootloader will not be used. It adds complexity to the code and the bootloader itself needs to be initially programmed. As a result, many micros are programmed using ICSP. Some projects include the necessary ICSP interface as part of the design (ie, it’s incorporated into the PC board). Otherwise, you will need to remove the PIC micro from its socket and program it externally. What’s needed Assuming you have your target device (ie, the PIC micro), you will need the following: a PIC programmer, a PC with suitable software and a breadboard if your programmer does not have a ZIF (Zero Insertion Force) socket. The programmer we recommend to start with is the PICKit3, which is a low-cost USB programmer (and debugger) from Microchip. There are other more expensive programmers available and they usually have advanced features that the PICKit3 lacks, such as bulk programming and better debugging options. That said, the PICKit3 is suitable for all hobby work and for prototyping and development. It’s portable, inexpensive and can even provide power siliconchip.com.au 11 32 Vdd 100nF 10k Vdd MCLR (ICSP) 1 1 2 3 40 IC1 PGD/RB7 PIC18F4550 39 PGC/RB6 Vss SC 4 PGD PGC AUX Vss 12 2010 Vdd GND 5 6 NC Vpp/MCLR 31 PROGRAMMING EXAMPLE Fig.1: this diagram shows a typical connection to a PIC18F4550. The pin-outs for different devices will vary and you should consult the relevant data sheet. to your target board (through the USB). The PICKit3 can program almost all Microchip microcontrollers and its firmware can be upgraded to enable support for future devices. The device itself is based on a Microchip microcontroller and it can update its own internal firmware using RTSP. This is an important feature because the programming algorithm for a future device may change (different Microchip microcontrollers have different programming requirements). No ZIF socket The PICKit3 does not have a ZIF socket. Instead, you connect its three programming lines plus two power supply lines to the target PIC. That’s five lines in all and this is simple to breadboard up on a prototype board. The programming lines are PGC, PGD and bar-MCLR/VPP. PGC is the clock line, PGD is the data line and bar-MCLR/VPP is the reset (Master Clear)/Programming voltage line. Note that these lines are common to all Microchip micros, so if you are using a different programmer, it also will have these lines. Fig.2: this window from MPLAB shows the which programmers support a selected device (here, a PIC18F4550). A green dot indicates that the device is supported. lent) does not have a ZIF socket, so a breadboard adaptor is used to connect to the target device. The PICKit3 has six lines (of which five are used) and these can be accessed using a single inline 6-way pin strip. In our case, we made a custom PC board to accept this pin strip (see photos) but it can just as easily be made up on a small piece of Veroboard (0.1inch grid). As shown in the photos, the 6-way pin strip is soldered to the top of the board. Two additional pin header strips are then soldered to the underside of the board – one to make the connections between the PICKit3 programmer and the breadboard and the second to ensure that the assembly is stable when the PICKit3 is connected. Step 2 – Making The Hardware Connections: install the PIC micro (henceforth referred to as the “target device”) on the breadboard, then download its datasheet from the Microchip website. TOP VIEW We are assuming here that you have a DIP (dual in-line package) device. The datasheet contains the pinout information you will need to connect the programmer to the target device. Although there is variation in the pinouts across and within Microchip families, the lines listed in Table 1 (if present) must be connected. Note that, depending on the device, these lines may be labelled differently. For example, some devices have multiple PGC/PGD pairs, which are then labelled with a numerical suffix (eg, PGED1, PGEC1). If there is more than one pair, any pair can be used for programming. However, only one can be used for debugging (this is set by writing the configuration words of the microcontroller). We are not going to cover debugging using the PICKit3 here. A typical programming connection diagram (ie, device to PICKit3) is shown in Fig.1. It uses a 10kΩ resistor BOTTOM VIEW Step-by-step programming Let’s now go through the programming procedure step-by-step. We’ll assume that you’re using a PICKit3 programmer and a breadboard. Step 1 – Making The Breadboard Adaptor: as mentioned, the PICKit3 (or equivasiliconchip.com.au A 6-way pin header is required to connect the PICKit3 to the breadboard. You can make one up on a small scrap of Veroboard. July 2010  27 The PICKit3 programmer is available from Microchip Direct – www.microchip.com/ The catalog number is PG16430) and the price is $US44.95 plus postage. This photo shows how the PICKit3 is connected to the breadboard (and to the target device) via a pin header socket. Fig.3: this “Output” window shows the PICKit3’s startup sequence. The error given means that the PICKit3 did not recognise any device, in this case because power had not yet been applied. Fig.4: when power is applied to the target device via the PICKit3, it recognises the device and shows its ID revision number. This also indicates that commun­ ication between MPLAB and the target device (via the PICKit3) is good. to pull up the bar-MCLR/VPP line to the supply rail VDD and some 100nF bypass capacitors on the supply lines. Avoid using capacitors on the VPP, PGC and PGD lines, as these will affect the high-speed digital signalling on these lines. In addition, the PGC and PGD lines have internal pull downs in the PICKit3, so don’t use pull ups on these lines. As shown in Fig.1, they are con28  Silicon Chip nected directly to the PICKit3. Note that the supply rail for different microcontrollers will be different. Usually devices with an “L” in the part number are low voltage (eg, 18LF1320). The power for programming can be supplied by the PICKit3 itself but you have to enable the power output separately, as described later. For now, it’s just a matter of connecting the relevant pins on the target device to the adaptor on the breadboard using wire jumpers. Note that the PICKit3 can supply up to 30mA at between 1.8V and 5V to the target device, which should be sufficient for programming (note: this may be insufficient for debugging if using the PICKit3 as the only power source). Note also that no separate system clock is required for programming – the clock signal supplied by the host (ie, the PICKit3) via the PGC line is sufficient. Step 3 – Installing PC Software: suitable PC software is required to drive your programmer. Many programmers are supplied with their own software while the PICKit3 uses MPLAB. This IDE (Integrated Development Environment) is free and can be downloaded from the Microchip website at www. microchip.com MPLAB is a 32-bit Windows application but will also run on 64-bit Windows versions. The screen grabs shown in this article are from MPLAB v8.50. Future versions may be different. Step 4 – Connecting The PICKit3: the PICKit3 connects to your PC using a USB cable (supplied with the programmer). Assuming you have already installed MPLAB, the driver will be found and installed automatically as soon as the PICKit3 is connected. Once that is done, you can connect the PICKit3 to your target device using your breadboard adaptor. Note that Pin 1 of the PICKit3 is indicated by a white arrow (see photo). Step 5 – Programming: once the connecsiliconchip.com.au tions are complete, MPLAB is used for programming via the PICKit3 (it can also be used for development and debugging). You will need the new firmware program for the target device and this is usually supplied as an Intel HEX file (extension .hex). The programming steps are as follows: • Start MPLAB, then go to Configure -> Select Device and select the correct device type. For example, if you are programming a PIC18F4550 microcontroller you need to select it here. Whether or not PICKit3 can program your device will be indicated by either a green or yellow dot (see Fig.2). A green dot means that the target device is supported, while a yellow dot means beta (ie, not fully tested) support. A red dot means the device is not currently supported and you won’t be able to use the PICKit3 to program that device. • If the device is supported, enable the programmer by going to Programmer -> PICKit3. This will bring up a dialog box similar to Fig.3. • Enable the PICKit3 to provide power for your device. To do this, go to Programmer -> Settings, click the Power tab and check that the correct voltage for your target device is indicated in the voltage group box. Usually MPLAB will set this to the default for the selected device. If there is a range of valid voltages, the lowest will be selected. If the voltage is incorrect, change it to the correct value. Now click the “Power Target Circuit from PICKit3” checkbox to enable the PICKit3 to power the device and click OK. If all is well, the PICKit3 will recsiliconchip.com.au Fig.5: this screen grab from MPLAB shows the contents of the program memory. The HEX file is parsed and the program memory is then loaded with the firmware image. Fig.6: the “Output” window now shows the result of programming the device, in this case a PIC18F4550 device. MPLAB will program and verify the image. The “Programming/Verify complete” message indicates all is OK. ognise the device, as shown in Fig.4. Here, the last line shows the Device ID (Silicon) revision, indicating that communication between your PC and the target device (via the PICKit3) is good. • Go to File -> Import. An Open File Dialog will appear and select the “All Load Files” in the Files Type field. This includes the “.hex” file extension. • Navigate to the new firmware file and open it. MPLAB will now decode the HEX file. You can see the contents of the memory by going to View -> Program Memory, as shown in Fig.5. • Finally, go to Programmer -> Program to program the HEX file to your target device. MPLAB will erase the device, then program it and finally verify the image. If all goes well, you should see a dialog as shown in Fig.6. Your device is now programmed and SC probably running. July 2010  29