Clifton Laboratories 7236 Clifton Road  Clifton VA 20124 tel: (703) 830 0368 fax: (703) 830 0711

E-mail: Jack.Smith@cliftonlaboratories.com

Introduction
Micro_Engineering_Labs_USB_Programmer
Micro_Engineering_Labs_X1_Development_Board
OLIMEX_Development_Board
Basic_Micro_2840_Development_Board
Microchip_MPLAB_ICD_2_
Other_Development_Boards
My__Recommendations

Before discussing specific hardware, it's first necessary to understand how a PIC is programmed. (PICs are one-chip microcontrollers. For more information, see my book (linked at Book). My discussion is, moreover, limited to the PICs developed by Microchip. I'll also limit my discussion to the later version 16F and 18F 8-bit line of flash memory PICs, as  those are  the ones I'm most familiar with.

Flash memory PICs (identifiable by the "F" in the part number, such as a 16F877, or an 18F4620) keep their program code in non-volatile electrically alterable "flash" memory. Wikipedia has a decent summary of what flash memory is and how it works at http://en.wikipedia.org/wiki/Flash_memory but for our purposes the important elements of flash memory are:

• It is electrically alterable and erasable
• It requires no power to maintain its values (non-volatile) over a reasonable lifetime (commonly said to be 40-50 years)
• It has a limited number of read/write cycles,  but for Microchip's products this number is sufficiently large as to not be a practical problem (in the hundreds of thousands of cycles

The programming process starts, of course, with a program. The program may  be written in a high level language, such as Swordfish BASIC, or in assembler. The diagram below presents a generic version of how a program goes from human cognizable form into the PIC. If written in assembler, the top block is replaced with the assembler's IDE. (IDE is integrated development environment, and is the program that integrates a text editor with the compiler or assembler functionality.)
 

The loader program, running on the PC, transfers the hex file data to the programmer hardware, which in turn, moves the data into the PIC where it is saved in flash memory.

The programmer-PIC interface is generally accomplished through "high voltage programming," in this case "high voltage" meaning a voltage above the normal PIC supply voltage. A typical programming voltage is 12V, whilst the PIC normally runs with 5V, or 3.3V. Microchip has changed the specific transfer protocol relatively frequently and hence the programmer is itself updateable. High voltage programming requires the programmer be able to control both the voltage applied to the master clear pin and the PIC supply voltage.

Most new PICs also have a "low voltage programming" mode whereby the code may be transferred using only the PIC's normal supply voltages. The programmers discussed in this page, however, are all high voltage programmers.

The electrical and data flow specifications for programming that Microchip commonly issues a separate data sheet just covering programming for a particular group of chips. For example, members of the 18Fxx8 family, such as the 18F458, use the following pins during programming:

The prototype boards discussed in this page are arranged for automatic connection of the correct pins when used with a compliant programmer. Except during the actual programming cycle, RB5 and RB6 are available for their normal use, although there may be limits upon what can be connected to these pins.

This arrangement is called ICP or "in-circuit programming" in that the PIC may be programmed without removing it from the development board and associated components.

A second method of programming the PIC, and one that I  generally use, is through the PIC's serial port and a "bootloader" program.

Most PICs have internal serial hardware allowing them to communicate with a PC using the PC's RS232 port. Level shifting hardware is required, of course, to convert the PIC's logic-level input/output to the bi-polar RS232 standard, and all the development boards examined on this page have the necessary level shifting hardware.

The bootloader program is a small program resident in the PIC that accepts data from the PIC's serial port and writes the data into the PIC's program flash memory. Thus, if the PIC has the necessary bootloader software, and with corresponding software on the PC, a hardware programmer is unnecessary. However, it's important to understand several shortcomings of bootloader programming, based upon my experience with Swordfish's bootloader code:

• The bootloader is specific to each PIC type and clock speed.
• A PIC cannot be purchased from Microchip with bootloader code installed, so you must have access to a high voltage programmer to install the bootloader program. The bootloader software prevents itself from being written over, so the bootloader need be installed only once.
• Swordfish has very good integrated support for the bootloader, but this may or may not be true for other compilers and assemblers.
• In order to use the bootloader, the PIC circuit must have a serial connection to the PC. This is not an issue with the development boards, but might be in a real circuit.

I should add that Swordfish comes with bootloader code files (hex files) for a variety of common PICs and clock speeds.
 

Micro Engineering Labs USB Programmer

The high voltage programmer I use is Micro Engineering Lab's USB programmer, illustrated to the right. The connector at left center is the USB port, whilst the 5x2 header pin connection at the right goes to the PIC or the development board.

The version I have includes a plastic case, which I highly recommend as a safety measure when working on bench with odds and ends of wire, components and the like.
 

In addition to the enclosure, I also purchased the optional ZIF (zero insertion force) socket adapter and  the short 10-pin jumper cable.

The ZIF adapter permits programming just the PIC, without a development board. I use this combination to install Swordfish bootloader software in a PIC as well as to program the chips associated with my Z100 tuning aid kit.

The first USB programmer I purchased was from mikroElektronika. It proved to be essentially unusable as it consumed 100% of my computer's USB  resources and would not release them without rebooting the computer. I've read that mikroElektronika's current USB programmer is redesigned to avoid this problem, but I have not independently verified this.

In contrast, Micro Engineering Lab's USB programmer has worked flawlessly since the beginning. I highly recommend it. The configuration I have has a current price of $145, which includes the Windows-based control program.
 

Dave, W6OVP, recently asked me to look over a used Micro Engineering Labs X1 development board, he purchased on E-bay, pictured below.
 

I removed a few parts from the "experimenter's area" of his used X1, restored some cut traces and installed sockets for easier access to the PIC's pins. This board is advertised for 16F-series PICs, but in fact it works with many 18F-series chips as well, since Microchip's 18-F parts generally are pin-compatible, although the 18-F parts will usually have extra functionality and significantly improved performance.

In using the X1 for a week or so, I've found it to be an excellent product and well suited for its intended purpose, learning how to program PICs. The photo at the right shows Dave's X1 board with my USB programmer connected to its programming port.
 

The idea behind the X1 and similar boards from Microchip and others, is that many common components are installed on the PCB and connected to the PIC. In some places, components are not provided, such as a  temperature sensor, but the board has pads where the user may install the components if desired.

I wrote a short Swordfish program, for example, to display integers from 0 to 255 on the LCD in decimal (d), hexadecimal ($) and  binary (b) in an endless loop. Each time the digit increments, a short 1000 Hz beep is sounded using the X1's miniature speaker.

Since no wiring or jumpers were required with the X1, this allowed me to concentrate on the code.

For a beginner desiring to learn how to program a PIC, the X1 is an excellent choice, albeit a bit on the expensive side with a list price of $200. If, on the other hand, your primary interest is developing circuits using a PIC, or don't wish to spend $200, other options exist.

I used the USB programmer to enter the code a couple of times to verify that functionality of Dave's used X1, but then I loaded the 18F458 PIC with Swordfish bootloader code and did  the remainder of the program development over the serial interface.

If MEL's X1 board is one extreme of integration of PIC and experimenter's parts, Olimex's board, pictured below, is the opposite.
 

The DEV-21 board includes a serial port with level converter chip, power connector, reset switch, 20 MHz crystal (in a socket), regulator for PIC power (+5 or +3.3 V, selectable via a jumper) and a 6-pin connector for ICP, although not compatible with MEL's USB programmer.

The extra PCB space is intended for circuit development via soldering to isolated pads.

I'm not a fan of this style of circuit development, but rather prefer solderless "plug board" providing the desired circuit speed permits.

I've had these boards for several years, acquiring them when learning MBASIC, Basic Micro's compiler for 16-F series chips.

Basic Micro also has a high voltage programer, the ISP-Pro, currently in version 3.0.

If you intend to program 16F chips only, Basic Micro's MBASIC, the 2840 development board and ISP-Pro are a good combination. 

You should also be aware that I've received several recent (summer 2008) reports of prospective purchasers having a very difficult time contacting Basic Micro via E-mail or telephone. In addition, I do not believe MBASIC is currently supporting 18F series devices, although I understand 18F support has been "in the works" for several years.

When used with the ISP-Pro, the 2840-board supports ICP. However, the ISP-Pro is incompatible with Swordfish, even though it will program many 18F chips.

When I say incompatible, I mean that it does not integrate with Swordfish's IDE so that one may compile a program and load it into the PIC via single key press or mouse click. It remains possible to have Swordish's hex file output manually loaded into a PIC using ISP-Pro. The lack of integration is because Basic Micro's control software is not a separate program accessible by other IDEs but rather is integrated as part of the MBASIC compiler.

When using the 2840 boards with 18F parts and Swordfish, I first program a suitable bootloader version into the 18F PIC using the MEL USB programmer and ZIF adapter. I then put the PIC with bootloader into the 2840 board and program in the Swordfish code using the bootloader. This step can be done with a single mouse click in Swordfish, plus the extra step of pressing the reset button on the 2840 board.

There is a line of development boards from China sold on E-bay amongst other places with similar features to the X1 board. I have no idea how good or bad they are, nor how well they integrate with programmers such as the MEL USB device. However, since they have serial interface ports, a bootloader approach should work with Swordfish compiler, assuming, of course, one has a way of getting the bootloader code into the PIC.

Microchip also has a line of development boards that should be considered. Their ICP interface is intended for the ICD 2 which will not, as mentioned above, easily integrate with Swordfish's IDE. However, programming via bootloader and serial port should be possible, assuming, of course, one has a way of getting the bootloader code into the PIC.

If you are a beginner wishing to learn how to program a PIC with a modern high quality compiler, I would purchase the following:

• Swordfish Compiler licensed version
• ME Labs USB programmer with enclosure and 28-40 pin ZIF socket

This combination allows you to then program bootloader code into a wide variety of 18F-series chips, thus allowing you to use any of the development boards described at this page, based upon your desires. If price is not an object, ME Lab's X1 board is an excellent choice for the beginner. If you know your way around a PIC, then perhaps the inexpensive Olimex board will be suitable when used with a auxiliary solderless board.