PICProto USB

The reader response to my column titled “A P89C668 Development Board for 8051 Fans” was enough to tell me that the BASIC programming language is—as it relates to the 8051, PIC, and AVR—alive and well (Circuit Cellar 151). ME Labs offers a good PIC BASIC compiler called PicBasic. I got a copy of PicBasic Pro because it’s more than a decent BASIC compiler. The professional version is relatively inexpensive, and it supports Microchip’s flavor of low-speed USB, which is driven by the PIC16C745 and PIC16C765 microcontrollers.

The PICProto USB development board was refreshing because I had to build it completely from scratch. I had to fly in two components, a 6-MHz ceramic resonator and a series-B USB connector. Otherwise, the through-hole assembly process was quick and easy. A schematic and bill of materials are included with the bare silk-screened PICProto USB PCB.

For a complex interface, the USB hardware is just as simple as basic RS-232 hardware. In fact, I’ll go out on a limb and say that a PIC-based USB hardware interface is actually simpler than a PIC-based RS-232 hardware interface.

The PIC16C745 and PIC16C765 USB microcontrollers are self-contained and don’t require any of the auxiliary level-shifting circuitry that is common for true RS-232 implementations. Using the PIC16C765 or PIC16C745, a bare-bones USB hardware interface consists of the PIC, a couple of 0.1-µF bypass capacitors, a VUSB filter capacitor, a ceramic resonator, a resistor, and the series-B USB connector. Even though the PIC USB solution provides for a simpler hardware interface, USB communication requires much more effort to implement.

On the PICProto USB development board, the 28-pin PIC16C745 IC socket lies inside the 40-pin PIC16C765 IC socket. I wanted to be able to mount either the 40-pin PIC16C765 or the 28-pin PIC16C745 on the PICProto USB development board. So, I used machined header pins to populate the 40-pin socket pads instead of a standard 40-pin socket. This allowed me to solder a standard 0.3² 28-pin socket inside the 40-pin socket footprint. My completed PIC-less PICProto USB development board is shown in Photo 3.

Photo 3—All of the goodies that complement the everyday PIC are included with this board. There are a couple of potentiometers, a pair of LEDs, and two push-button switches. The 25-pin connector pad layout suggests that a serial-to-USB thing could happen in the prototype area.

Because there is no “F” in their names, the PIC16C745 and PIC16C765 microcontrollers are available as either windowed ultraviolet erasable parts or one-time programmable (OTP) parts. I have a fancy timer-equipped EEPROM eraser, but I’ve been spoiled by the easy-to-program, flash memory-based PICs. Because the new generation of flash memory-based USB PICs wasn’t available when I started this article, I used the MPLAB ICE 2000 and a PCM16XQ1 processor module to stand in for the windowed PIC16C745 and PIC16C765.

Before attempting to read the PIC-Proto USB development board’s USB datastream with the USB Tracker 110, it may be a good idea to check to see if all of the solder joints took. A small USB demo program that moves the test computer’s cursor is included with the PicBasic Pro compiler. I loaded that puppy into the MPLAB ICE 2000 to see if I could twirl the cursor.

Using the MPLAB ICE 2000 instead of the real thing required that I invoke the MPLAB IDE. Normally, that would have meant loading and running a separate IDE for the PicBasic Pro compiler. Not in this case. The PicBasic Pro compiler is capable of running as a language toolset within the latest version of the MPLAB IDE. Although being able to run PicBasic Pro and MPLAB in a single IDE is a good thing in terms of development, there is another upside to this union: PicBasic Pro generates a standard .cod file that allows for debugging using the MPLAB ICE 2000 hardware.

After plugging in the MPLAB ICE 2000 PCM16XQ1 USB processor module and attaching a 40-pin DIP device attachment module to the end of the processor module’s cable, I carefully plugged the MPLAB ICE 2000 device attachment’s gold-plated 40-pin DIP header into the 40-pin header socket that I had installed on the PICProto USB development board. Then, I jumpered the PICProto USB development board for USB-supplied power.

At that point, I loaded the PicBasic Pro USB demo, USBMOUSE.BAS, in the MPLAB IDE. I couldn’t get a good reset on the MPLAB ICE 2000. After clicking the MPLAB IDE Run icon a few times without success, I figured that something wasn’t working correctly.

I first took the software problem determination route. (After all, my soldering should be perfect.) I muddled around, trying this and that with files and such with no joy. OK, maybe I did have a problem with the PICProto USB development board hardware. So, I disconnected the PICProto USB development board and took it to the bench for a look under the magnifier. As I had expected, all was well with the soldering job and component placement.

 I did not cut any of the default jumpers on the PICProto USB development board. The only live jumper pins were the power-source pins. I decided to reattach the MPLAB ICE 2000 and move the powered-by jumper from USB to external. The MPLAB ICE 2000 reset was successful, and I was able to configure the MPLAB ICE 2000 to use the PICProto USB development board’s power and clock. Obviously, the emulator and associated electronics drew a bit more current than the USB was willing to supply at that point. Despite the little drawback, it was good.

I had already created a project directory and copied the USBMOUSE.BAS file into it. A study of the USB documentation that was included with the PicBasic Pro compiler indicated that I would need to add supporting files to the project as well. These files, which were included with the compiler, provide a basis for the USB hardware layer that is intended to reside in the PIC firmware. The PicBasic Pro USB support files are based on the original Microchip USB support files and have been modified to compile under PicBasic Pro.

Having put my emulator hardware problem behind me, I was on my way to compiling the USB demo code and controlling a cursor. Well, not quite on my way. I clicked the MPLAB IDE’s Build icon and was greeted with what seemed to be a million error messages, which wasn’t good.

My first clue was the first error, which stated that it could not open a particular include file, P16C765.INC. That’s easy enough, I said to myself. I’ll just rename the PicBasic Pro 16C765.INC to P16C765.INC and things will once again be good. Ha! My mouth was still open when the dust stirred by a million more error messages had settled. OK, maybe the list file would reveal an answer. Duh. My second clue was on the first error line of the listing. MPASM header was the comment beside the lost P16C765.INC file.

You can configure the PicBasic Pro to use either the MPLAB assembler (MPASM) or the internal PicBasic Pro assembler (PM). Well, there’s a big check mark in the “Use MPASM Assembler” box under the MPLAB IDE’s project build options. I had renamed the PM include file (16C765.INC) to fool the MPLAB IDE assembler, but the MPLAB IDE assembler didn’t bite on the contents of the newly monikered file.

I checked my Win2K path variable and indeed the entry for the Microchip MPLAB IDE include files was there. Without question (I was desperate), I simply copied the Microchip-provided MPLAB IDE P16C765.INC and P16C764.INC include files into my PicBasic Pro USB project directory.

Here we go. After clicking on the MPLAB IDE Build icon, I was humming my favorite Bob Marley tune, “Jammin’.” After another click on the MPLAB IDE Run button, I was growing dreadlocks. The test machine’s cursor was going in circles and dancing to the reggae beat. It was good indeed.