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FIGURE 15-9 All the parts of the final BS2 s serial communications/programmer interface can be soldered as one assembly. Notice that the wires all bend together to provide an easy and direct interface to the BS2.

Serial Communications/Programming Interface Parts List Female nine-pin D-shell connector 0.1 F capacitors (any type) 24 gauge wire, different colors

When you ve assembled the serial communications/programming interface, cut a strip of the two-sided tape off the back of a small breadboard and stick on a three or four AA battery clip. For the BS2 to work properly, 4.5 to 6 V must be applied to it. If you are going to use alkaline cells (which produce 1.5 to 1.8 V each), only three batteries are required. If you are going to use NiMH rechargeable batteries (which produce 1.2 V), then four batteries will be required. You might also want to put a power switch in line with the positive voltage from the battery pack. The positive and negative voltage should be connected to the common strips on the breadboard and connected to VDD (pin 21) and VSS (pin 23), respectively. VIN and the on-board voltage regulator is bypassed as is the _RES (Reset) pin. The BS2 will power up any time power is applied to it. With the hardware together, you can download the BASIC Software Editor (from www.parallax.com, Downloads ) and install it on your PC. Along with Windows software, there are also Linux and Mac editors available. The editor should install like any other application and once you have connected the serial port to a straight-through nine-pin male to nine-pin female cable, you are ready to try out your first application! The typical first application of any computer system is the Hello World, which follows. This program will simply print out the welcome phrase to indicate that it is up and running. Key in the program to the BASIC Stamp Editor, save it on your PC s desktop, and then either click on the right-pointing triangle on the toolbar or press Ctrl-R. This will compile, download, and then run the application.

' Hello World ' ' This Program Prints the String "Hello World!" ' ' ' Author: Myke Predko ' ' Date: 05.06.23 ' ' '{$STAMP BS2} '{$PBASIC 2.5} ' Variables ' Mainline DEBUG "Hello World!", CR END ' ' Print the String Stop Program

If the program was keyed in correctly and the wiring is correct, a terminal Window should appear with the message Hello World. If there is an error message indicating there is a problem with the program, check what you ve keyed in to make sure the program has been entered correctly. If the PC cannot find a BS2 connected to it, check the wiring of the nine-pin D-shell connector and that at least 4.5 (but not more than 6.0) V is going into the BS2 s pin 21 and 23. Additional debugging information can be found in the BASIC Stamp Syntax and Reference manual downloadable from the Parallax web site.

With the software loaded on your PC and a simple programming/communications interface built and tested for your BS2, you can now start experimenting with the input/output capabilities of the microcontroller. The most fundamental output device that is used with a microcontroller is the light-emitting diode (LED) and with it you can learn a lot about programming and how the BS2 works. To demonstrate LED interfacing in this and the next section, you should wire the circuit shown in Fig. 15-10, consisting of the BS2, the programming/communications interface, and eight LEDs, wired to the low eight bits of the BS2 s I/O port. The parts required for this circuit are listed in Table 15-6. To simplify the wiring in the prototype, eight 5 2 mm rectangular LEDs were used instead of square LEDs (Fig. 15-11). The first task you might want to perform is to flash a single LED (we ll get to the other LEDs later in this section) by performing a delay, turning the LED on, waiting the same delay, and turning the LED off. This process is repeated using the DO/LOOP statements. The first program, listed here, writes directly to the P0 I/O pin to turn the LED on and off with delays in between, as described in this paragraph.

' LED Flash Demonstration 1 - Flash LED on P0 2 per second '{$STAMP BS2} '{$PBASIC 2.5} ' Mainline DIR0 = 1 DO OUT0 = 0 PAUSE 250 OUT0 = 1 PAUSE 250 LOOP