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Cheap programmer for the PIC32 microcontroller By Robert Rozée, M.E. (EEE) Want to build a recent SILICON CHIP project that uses a PIC32? Great . . . but the prospect of programming a PIC32 can initially seem daunting. This minimal programmer will upload firmware into a PIC32 quickly and simply at very low cost. W ITH THE DEMISE of parallel and “real” serial ports on PCs, getting code into Microchip’s PIC processors has in recent years become more complicated and expensive. Way back in the 1990s, you only needed a few resistors and a transistor to build a lowcost PIC programmer, and hobbyists around the world spent many a joyful hour creating interesting gadgets with these little computers. Sadly, those simple programmers no longer work with today’s USB to serial bridge adapters and a PICkit 2 or PICkit 3 became essential. Then there is the large and somewhat complex MPLAB X IDE (400MB download) needed to drive Microchip’s programmer. These are somewhat daunting requirements for a user looking to program a single PIC for the first time. Compare this to the popular Arduino platform. Every Arduino board comes with a serial bootloader pre-installed, hence code can be uploaded directly via a serial or USB port without the need for a specialised programmer. The software to write, compile and upload this code (the Arduino IDE) is “only” an 80MB download. Which was great – for a while. But then Geoff Graham released the Micromite – a complete BASIC computer on a PIC32 chip in a 28-pin DIP (SILICON CHIP, May 2014). It is significantly more poweful than most Arduinos but the higher cost of programming equipment is a drawback. While the blank chip for a Micromite costs less than US$5, uploading the Micromite firmware required a programmer costing as much as 10 times more. That isn’t a big deal if you plan to program PICs frequently but it’s a bit expensive as a one-off. Hence a group of intrepid mem- The PIC32 Processor Family The PIC32 family of processors, made by Microchip Technology Inc, are powerful 32-bit system-on-chip (SoC) devices containing everything required to implement quite complicated computers that are as powerful as the first IBM PCs. This from a chip that is available in a 28-pin DIP, costs less than US$5, and can run from a pair of AA cells. A number of SILICON CHIP projects in recent years have made use of PIC32 devices, including: the Colour Maximite (September 2012), GPS Tracker (November 2013), Micromite (May 2014, January 2015), and Nixie Tube Clock (February 2015). The Micromite (PIC32MX170 chip + 47μF capacitor and 10kΩ resistor) is especially notable as it is programmed in BASIC, allowing the hobbyist to write simple code to realise almost any project without need for any sort of development environment beyond a serial terminal. 76  Silicon Chip bers from “The Backshed Forums” set about trying to create a cheaper, simpler alternative. The end result At the end of this (somewhat lengthy) effort lay a new set of extensions to pic32prog, an existing open source (GPL) command-line utility written and maintained by Serge Vakulenko. It works with a range of commercial PIC programmers – including the PICkit 2 (but not 3). The latest release of pic32prog is now also able to use an Arduino Nano, using a protocol dubbed “ascii ICSP”. Together with a few resistors and a 3.3V zener diode, this is sufficient to upload firmware to a PIC32. The total cost? Less than that of a single PIC32MX170 chip. The Arduino hardware and “ascii ICSP” protocol are needed as an intermediate step. This is because, even though a modern PC has lots of computing power, limitations in the way USB is implemented prevent direct access to the control pins (RTS, CTS, DSR, DTR) of a USB-to-serial bridge at any reasonable speed. Early attempts that connected directly between serial port pins and the target PIC32 resulted in programming times of several hours or extreme unreliability, whereas with an Arduino Nano in between, this time is cut to just a few minutes. The “ascii ICSP” protocol is very simple, accepting single-character siliconchip.com.au USB CABLE FROM HOST ICSP TO TARGET 3 x 100 Ω D13 D12 +3.3V D11 Vcc D10 GND USB PORT AREF A0 D9 A1 D8 A2 D7 A3 D6 A4 DISABLE RESET FROM USB PORT D4 A6 D3 A7 3.3k A ZD1 3.3V 1W PGD PGC NC ZD1 A D2 K GND RST RST GND RxD VIN TxD SERIAL I/O Fig.1: the circuit is based on an Arduino NANO module. All you have to do is add a few resistors, a 3.3V zener diode and some pin headers. Power is supplied from the USB host (ie, a PC) via the Arduino Nano’s USB port. LOW-COST PIC32 PROGRAMMER USING AN ARDUINO NANO Hardware The hardware is simple and cheap, the most expensive part being an Arduino Nano, widely and cheaply available via eBay. Three 100Ω resistors and a 3.3V zener diode create a switchable 3.3V supply for the PIC32 being programmed, capable of delivering up to 50mA ((5V - 3.3V) ÷ 33Ω) to the device. This load is shared across three pins on the Arduino, each capable of delivering 20mA. Two more resistors (3.3kΩ) provide pull-ups for open-collector outputs that drive the two programming pins on the target PIC32 – PGC (clock) and PGD (data). These two pull-ups go to the 3.3V supply – while the Arduino Nano is a 5V device, most of the PIC32 siliconchip.com.au VIN 29 IN OUT +5V REGULATOR GND RESET/PC6 SCL SDA RESET AREF RESET +5V +5V GND 4 17 +3.3V D1 1 2 3 4 5 MINI USB-B 20 TX LED VccIO 3.3V OUT λ MOSI/PB3 CBUS1 23 16MHz D+ 7 8 RXD TXD ATMEGA 328P (32TQFP) 22 USB INTERFACE 16 D– CHIP 15 SCLK/PB5 MISO/PB4 CBUS0 VUSB RX λ LED 5 1 TXD/PD1 A6 A5 A4 A3 A2 A1 A0 PB1 XTAL1/PB6 PB0 XTAL2/PB7 PD7 PD6 RXD/PD0 A7 PB2 22 19 28 27 26 25 24 23 PD5 ADC7 PD4 ADC6 PD3 ADC5/PC5/SCL PD2 ADC4/PC4/SDA TXD/PD1 ADC3/PC3 RXD/PD0 17 16 15 14 13 12 11 10 3 2 1 32 31 30 D13 D12 D11/ PWM D10/ PWM D9/ PWM D8 DIGITAL I/O POWER ASCII commands from a host computer (running pic32prog) and converting these into the clock (PGC) and data (PGD) signals needed to program a PIC32. Lower case letters d, e, f, & g cause clocked output of the bit pairs 00, 01, 10, and 11 respectively, while upper case letters D, E, F & G clock out the same pairs, then read back one bit. Other commands carry 4-bit pairs encoded as a single letter, assert and release the reset (-MCLR) pin and turn on/off the 3.3V supply to the target PIC32. Between PC and Arduino, serial communications occur at a brisk 115,200 baud. ANALOG INPUTS SC 20 1 5 K 3.3k D5 A5 +5V DISABLE 328P FOR USE AS A SERIAL BRIDGE ARDUINO NANO MCLR D7 D6/ PWM D5/ PWM D4/ PWM D3/ PWM D2/ PWM D1/ TXD D0/ RXD ADC2/PC2 ADC1/PC1 ADC0/PC0 Fig.2: block diagram of the Arduino Nano module. It’s based on an Atmel ATmega328P microcontroller chip and a USB interface chip. pins should never have over 3.3V applied. No pull-up is fitted to the opencollector -MCLR (reset) output, as a 10kΩ pull-up should normally be present at the PIC32 end. In operation, programming data is exchanged with the PIC32 in a 4-phase cycle. In phases 1 & 2, data (2 bits) is written to PGD. In phase 3, the direction of PGD is reversed to allow a single data bit to be read back from the PIC32, then in phase 4 the direction of PGD is reversed again. Uploading the 250kB of Micromite firmware to a PIC32MX170 processor involves sending over three million November 2015  77 D13 USB PORT D12 +3.3V D11 AREF D10 D9 17 A0 25 ATMEGA 328P A3 JUMPER SHUNT MCLR PGD D6 1 A4 D8 D7 9 A1 A2 D4 A6 D3 D2 A7 RST 100Ω 100Ω 100Ω D5 A5 +5V Fig.3: install the parts on the Veroboard and connect it to the Arduino Nano as shown here. Note that the tracks at the righthand end of the board are all connected together. ARDUINO NANO 3V3 PGC GND RST GND RxD VIN TxD Vcc 3.3k 3.3k ZD1 GND COUNTERBORE OR CUT ALL TRACKS AT THIS COLUMN OF HOLES characters out the serial port and receiving half a million. Building it The circuit is built on a small section of Veroboard attached to the side of the Nano, with a 5-way cable running up to a standard 6-pin ICSP plug. If desired, a LED and a 3.3kΩ series resistor can be connected across the 3.3V zener diode to show when the supply is turned on. A 3-way header should also be fitted to the Arduino Nano board to al- low linking its reset pin to ground or +5V. If the Arduino’s reset pin is linked to ground, the onboard ATmega328P processor is disabled and the board can be used as a simple USB to serial bridge (via the “serial I/O” connector shown on the schematic). If reset is linked to +5V, the firmware on the Arduino is protected from being overwritten and the programmer will be detected more quickly when pic32prog is launched. Do NOT install a jumper on these pins yet. Note: do not press the onboard re- Typical Programming Session C>pic32prog -d ascii:com5 mm47b32.hex Programmer for Microchip PIC32 microcontrollers, Version 2.0.174 Copyright: (C) 2011-2015 Serge Vakulenko (ascii ICSP coded by Robert Rozee) Adapter: Processor: Flash memory: Boot memory: Data: Erase: Loading PE: Program flash: Program boot: Verify flash: Verify boot: Program rate: . OK1 OK2 - ascii ICSP v1E MX170F256B 256 kbytes 3 kbytes 258692 bytes (90mS) done 1 2 3 4 (LDR) 5 6 7a (PE) 7b 8 v0301 ####################################### done ####### done ####################################### done ####### done 2086 bytes per second total TDI/TMS pairs sent total TDO bits received total ascii codes sent total ascii codes recv maximum continuous write O/S serial writes O/S serial reads (data) O/S serial reads (sync) XferFastData count 10mS delays (E/X/R) elapsed programming time 78  Silicon Chip = = = = = = = = = = = 3147141 pairs 459064 bits 987417 157828 452 chars 95940 14354 10 58902 9/0/0 2m 06s The tracks on the underside of the Veroboard must all be cut as shown in this photograph. set button while the reset pin is linked to +5V, as doing so will short the USB port’s +5V output to ground. Software The only software required is the pic32prog.exe executable itself (versions 2.0.174 or later) that can be downloaded from the pic32prog source repository at GitHub: https://github.com/sergev/pic32prog https://github.com/sergev/pic32prog/ blob/master/pic32prog.exe?raw=true Note: the second link goes direct to the Win32 executable. Mac OS X and Linux versions are also available. Drivers for the Arduino’s USB to serial bridge may also be required for Windows XP and earlier. In the case of Chinese clones of the Arduino Nano currently available on eBay, it’s likely that the bridge device used will be a CH430G, with drivers available from the manufacturer: www.wch.cn/download/CH341SER_ZIP.html The Arduino IDE is not required for loading the “ascii ICP” firmware onto the Arduino Nano, as this function is performed by pic32prog internally. Once the USB drivers have been installed, simply open a command window at the folder where pic32prog is located. With the Arduino attached to a USB port but no target PIC32 connected, type: pic32prog -d ascii:com5 -b3 where com5 is the serial port assigned to the Arduino, ascii is the name for the class of programmer (“ascii ICSP”), and -b3 tells pic32prog to upload the “ascii ICSP” firmware to the attached Arduino. This should display a message saying that firmware is being uploaded to the Arduino and will complete in a few seconds: siliconchip.com.au C>pic32prog -d ascii:com5 -b3 Programmer for Microchip PIC32 microcontrollers, Version 2.0.147 Copyright: (C) 2011-2015 Serge Vakulenko (ascii ICSP coded by Robert Rozee) 57600 baud ... synchronized Signature = 1e950f Device = ATmega328P ###################### Firmware uploaded to ‘ascii ICSP’ adapter OK If you see a row of dots after the “57600 baud” and a failure message, try repeating the process but this time press the Arduino’s reset button while the dots are being written. If this also fails, try using -b1, -b2 or -b4 to select different Arduino bootloader baud rates. The vast majority of Arduino Nanos use a bootloader baud rate of 57,600 but there may be a few that use something different. Note that the above step to upload the “ascii ICSP” firmware to the Arduino Nano need only be performed once. You should then install a jumper between the reset and +5V pins. You are then ready to upload the Micromite (or other) firmware to your PIC32. Using it Place the firmware you want to upload in the same directory as pic32prog and open a command window at that location. Connect the target PIC32 to the programming hardware (Arduino). The target PIC32 needs to have all its ground pins connected together, all VDD pins connected, a suitable capacitor between the Vcap pin and ground, and -MCLR pulled up to VDD via a 10kΩ resistor. It is essential that (+3.3V <at> 26mA) ICSP FROM PROGRAMMER 100nF 10k 1 MCLR 2 Vcc GND PGD 26 25 24 PGC 23 IC1 PIC32MX170B PIC3 2 MX170B 22 21 9 VCAP 10 (TxD) 11 (RxD) 12 GND 20 MM CONSOLE TX 18 MM CONSOLE RX 17 16 14 47 µF 6V 15 AVSS 27 VSS 19 VSS 8 Fig.4: before programming, the target PIC32 microcontroller needs to be wired in a manner similar to this example PIC32MX170B (check the pin connections for your particular PIC micro). no ground or VDD pins be left disconnected. An example schematic for the PIC32MX170B 28-pin DIP is shown in Fig.4, including both ICSP and Micromite serial terminal connectors. The capacitor at Vcap should be a low-ESR type, such as chip ceramic or tantalum. If ceramic, the capacitor can be a 10µF part. To upload the PIC32 firmware, type: pic32prog -d ascii:com5 filename.hex where filename.hex is the name of the firmware file. The programming hardware handles supplying power to the target PIC32, turning the 3.3V supply on before commencing programming and turning it off when completed. Programming should take a few minutes, after which you can disconnect Useful Batch Files: Open a Command Window & List Serial Ports When using command-line utilities like pic32prog under Windows, there are a couple of batch files that are extremely useful to have sitting in the same folder. The first is a “command.bat” file, which, when double-clicked in a folder, will open a command window at that location. The “command.bat” file is as follows: <at>prompt $n$g <at>cmd The other useful batch file to have around is “ports.bat” to list the available serial ports on a Windows PC. While there are more complicated solutions, the simplest means of obtaining this information is from the Windows registry using the following lines within the “ports.bat” batch file: <at>reg query HKLM\hardware\devicemap\serialcomm <at>pause siliconchip.com.au PGD 7 TERMINAL Vcc MCLR 3 6 NC VDD 4 5 PGC 13 28 AVDD the programmer from your PIC32. On very rare occasions, pic32prog can throw an error during programming – this is usually due to spurious behaviour within the target PIC32 triggered by electrical noise from the programming PC’s power supply (especially if it’s a laptop). If this happens, just reprogram the device a second time and the error will almost certainly not re-occur. Laptop computers can produce more electrical noise when running on AC power, so running off the battery may be prudent if issues arise. Conclusion The combination of pic32prog and Arduino Nano provide a simple and cheap method for programming a PIC32 chip, albeit a bit more slowly than the PICkit 2/3 and without the integrated support in the MPLAB X IDE. Acknowledgements (1) “ascii ICSP” protocol and hardware designed by Robert Rozée. (2) “bitbang.c” extension for pic32prog written by Serge Vakulenko and Robert Rozée. (3) The Backshed Forums: http://www. thebackshed.com/forum/forum_topics.asp?FID=16 (4) Full details of the “ascii ICSP” protocol are available in the file ICSP_ v1E.ino at: https://github.com/sergev/ pic32prog/tree/master/bitbang (5) PIC32 programming details are from: “PIC32 Flash Programming SC Specification” (60001145N.pdf) November 2015  79