Make Electronics

Experiment 34: Hardware Meets Software

302 Chapter 5

Decoding    the Code

Let’s take a look at the little program that you typed in. The first line identifies

a section of the program. This program only has one section, and we’re calling

it “main.” Any word with a colon after it is the name of a section of a program:

main:

The second line tells the chip to send a high output from Logic Pin 1:

high 1

The third line of the program tells the chip to wait for 1,000 milliseconds. This

of course is the same as one second:

pause 1000

The fourth line tells the chip to change Logic Pin 1 back to its low state:

low 1

The fifth line tells the chip to wait for another 1,000 milliseconds:

pause 1000

The last line tells the chip to go back to the beginning of the “main” section:

goto main

1

2

3

4 5

6

7

8

PICAXE

08M

(Logic Pin 0)

Logic Pin 1

Logic Pin 2

Logic Pin 4

Logic Pin 3

Figure 5-138. The conventional pin numbers of the PICAXE chip are incompatible with the

numbering system that is used in the PICAXE programming language. To minimize confu-

sion, this guide refers to “Logic Pins” when using the numbering system that is required

for programming the chip.

In from Computer

Out to Computer

Digital Output Pin0

Infra-Red Output

Digital Output Pin1

Digital Input Pin1

Analog-Digital Converter Pin1

Digital Output Pin2

Digital Input Pin2

Analog-Digital Converter Pin2

Motor Power Output Pin2

Tune Output

Digital Output Pin4

Digital Input Pin4

Analog-Digital Converter Pin4

Digital Input Pin3

Infra-Red Input

1

2

3

4 5

6

7

8

PICAXE

08M

Figure 5-139. Many of the pins on the PICAXE 08M have multiple functions, which can be

selected by appropriate program instructions.

The program doesn’t use the usual

pin numbers on the chip. It uses

what I will call “logic pin numbers.”

Figure 5-138 shows how they are

numbered. Figure 5-139 shows their

multiple functions. I have put Logic

Pin 0 in parentheses because its main

purpose is to send data to the com-

puter through the USB cable. It can

do double duty as a digital output,

but you have to disconnect it from

the USB cable first. It’s easy to forget

to do this. It’s a hassle that I prefer to

avoid.