Introduction

fpicprog is a software driver for FTDI USB chips like the FT232RL to program Microchip PIC™ chips. Contrary to other such software, fpicprog allows fast programming and verification, by using the so-called Synchronous Bitbang mode of the FT232RL and later chips. Programming several kilobytes of program data takes seconds, where other FT232-based programming methods take minutes for the same data.

USB-to-serial converters with the FT232RL are readily available over the internet, often costing no more than a handful of dollars. These are typically not in a housing, but instead provide a circuit board with a USB connector on one end and a bare PCB header on the other. These are easily used with a breadboard to connect the PCB header to the appropriate pins of the PIC chip. Make sure however, that the converter uses the appropriate voltage for your PIC chip. There are versions at 5V and at 3.3V.

Note that fpicprog is designed to work with chips which provide Low-Voltage Programming, or Single-Supply programming. It is possible to use one of the pins of the FT232 chip to drive a high voltage, and thereby also use fpicprog for High-Voltage programming, but this requires extra circuitry which is not described in this document.

Supported chips

fpicprog supports chips in the following families: PIC10, PIC12, PIC16, PIC18 and PIC24. Most chips supporting Low-Voltage Programming from these families can simply be added to the device database by copying the relevant parameters from the datasheet. See the documentation in man/fpicprog-devlist.5.txt and the device_db folder for more details.

Compiling fpicprog

To compile fpicprog from the github repository, clone the gphalkes/fpicprog inlcuding the makesys submodule. Also make sure that you have the development package for libftdi (commonly called libftdi1-dev or libftdi-devel) and the google-gflags development package installed.

Then build fpicprog. Note that if clang++ is installed, the COMPILER=gcc can be left out to build with clang++ instead of g++.

git clone --recurse-submodules https://github.com/gphalkes/fpicprog
make -C fpicprog/src COMPILER=gcc

If you have cloned the repository without the makesys submodule, you can fetch the submodule using:

cd fpicprog
git submodule init
git submodule update

Setting up access to the USB devices for non-root users

On Linux systems, by default the programmers typically are only accessible by root. To make fpicprog able to access the programmers as a regular user, use udev rules to set the permissions on the programmer. The following example makes the programmers (with USB Product ID 0x6001) accessible to all users:

SUBSYSTEM=="usb", ATTR{idVendor}=="0403", ATTR{idProduct}=="6001", MODE="0666"

Depending on the device you are using, you may need to set the product ID to 6001, 6010, 6011, 6014 or 6015

Finding the programmer

To list the attached devices that fpicprog supports run the following command:

fpicprog/src/fpicprog --action=list-programmers

This requires that the programmers are accessible as the user the command is run as (see the previous section on how to set this up). To select the device to use, supply at least the --ftdi_product_id flag with the value that is shown in the listing (except for 0x6001, which is the default). If there is more than one device with the same product ID, also provide the serial number to the --ftdi_serial flag.

Connecting the programmer

Each PIC chip has a different pin layout, and there are different versions of Low-Voltage programming, thus wiring up the chip will require checking the datasheet for the chip you wish to program. However, in general you will need to at least make the following connections:

Programmer	Target
VCC	VDD
GND	VSS
TxD	!MCLR
DTR	PGC
RxD	PGD

(Note that this is for the default settings. You can instruct fpicprog to use different pins instead, if that makes wiring easier.)

Although not strictly necessary, it is recommended to connect the !MCLR pin to VCC using a pull-up resistor. You may also want to add capacitors between the VDD and VSS pins as recommended by Microchip, although I have been able to reliably program chips without any of these additional components.

An example of wiring up a PIC18F45K50 is in the picture below. Note that the order of the pins on the USB-to-serial converter is model dependent, so you will have to check your specific board for the exact pin layout.

Chips using a PGM pin

Some PIC chips use a PGM pin to enter programming mode, instead of a handshake using the !MCLR pin. If this is the case, you need to connect CTS -> PGM as well.

Split PGD pin operation

The default wiring can cause relatively high current to flow on the PGD pin, as it will be driven from both the FTDI chip and the PIC chip at the same time. Also, it has been found that using 3.3V for programming some of the F-series PIC chips that should allow operation at 3.3V (not all can, check the datasheet for the chip you are using), attempting to do so results in too low signal voltages and reading invalid values.

To overcome both these issues, it is possible to split the PGD pin use in an input pin and an output pin. To enable this, the --ftdi_PGD_in flag can be used the specify a different pin to use for reading the PGD pin. In this case, a series resistor of approximately 470 ohms must be connected in series with the driving pin of the programmer module, i.e. the pin specified by the --ftdi_PGD flag.

An example of wiring up a PIC18F25K42 with the seperated PGD signal to a FT4232H Mini Module on Channel A can be seen in this example. The example uses the RTS pin, which is not available on most FT232 modules. However, if the PIC chip doesn't need have a PGM pin, the CTS pin on the FT232 module can be used. This required the following flag combination: --ftdi_PGM=NC --ftdi_PGD_in=CTS.