Practical_Electronics-May_2019

 512 words of code, 24 bytes of RAM
 An internal oscillator calibrated to 1%
 8-bit timer
 4 I/O pins
 Wake on pin change
 SPI interface
 I^2 C interface
 UART interface
 1-wire interface
 Very low power consumption.

This now makes the processor a very
capable device – so long as your actual
requirements on what the device does
with those capabilities are not too de-
manding. Needless to say, you are not
going to be able to drive an LCD dis-
play with a parallel interface. But you
could drive a display equipped with a
serial interface, so long as you do not
need to display lots of text. All of that
text has to be stored in memory, and we
have just 512 bytes for Flash memory
storage. A serial LCD showing the time,
or perhaps the ambient temperature, is
probably feasible. Offering both? Perhaps
not – but half the fun is experimenting
and squeezing the maximum capability
from limited resources!
The memory layout of the device is
shown in Fig.2. Along with the gen-
eral-purpose registers – our available
RAM for program variables – there
are just eight special function regis-
ters. Here lies the PIC10F’s attraction
for other reasons – it is a very simple
device, and therefore makes an ideal
basis for learning the complexities
of a microcontroller. Other systems,
even the venerable Arduino processor,
contain far more registers, which may
overwhelm a student when trying to
master the lower levels of microcon-
troller systems. The PIC10F makes an
ideal entry point.
The pin-out of the fi rst device we
will be using is shown in Fig.3. This
variant is a dual-in-line plastic DIP
package, which is easy to solder to Ver-
oboard, or plug into a breadboard. The

pin-out shows how several functions

are mapped to the I/O pins.

Possibilities

So, what can you actually do with a

processor that is so limited, and with

so little memory?

First, remember that it is a very small

device – as can be seen in Fig.1. This

means it can be retrofi tted into an ex-

isting device or be used to create a tiny

functional product.

So what kind of projects are possible?

Here are some examples that spring

to mind that we believe are possible.

Smart bike light

Fitted with an accelerometer IC, the

PIC10F could be used to sense sudden

deceleration, and fl ash the brake light

automatically. A safety feature perhaps?

Disco lights

A string of RGB LEDs that change colour

depending on motion detected by an

acceleration IC. Could be fun on the

dance floor when mounted on your

best dancing shoes!

Logic probe

An improvement on an old classic –

a probe that can indicate when high,

low or pulses are detected on a wire.

Combined with an RGB LED for a more

modern approach to indicating the state.

We could program green for low, red

for high and blue for pulse.

Temperature warning

A small device that can be placed in

the refrigerator and warn when the

temperature rises too high. With some

additional components it should be

possible to detect a low-battery con-

dition too, and provide an additional

warning. A circuit like this could run

from a coin cell battery and be realised

in a very small enclosure.

Knock-knock switch

Making use of a simple piezo buzzer to

act as a vibration sensor, create a device

that will toggle a relay when a ‘knock-

knock’ physical signal is detected on a

surface. Ideal for turning desk lights on

and off, or as a general novelty switch.

Smart switch

A relay-controlled power source that

is controlled by a push switch. The

switch is de-bounced for a period of

time before turning on. While on, a long

press of the button will fl ash an LED

as a warning, and then power the relay

off if continued to be held. If a latching

relay is used, this circuit will consume

virtually no power, making it an ideal

way of controlling battery-powered

devices. It could also have a timer for

‘auto power-off’ functionality.

In this series of articles we will ex-

plore several of these ideas, and other

if suggested by readers – just pop your

thoughts into the magazine chat forum

at: http://www.eeweb.com/forum/category/

epe-magazine

We will explore circuits from

breadboard through to surface-mount

PCB designs to show the range of

applications.

Although these devices have at a

maximum only 512 words of program

memory, each of these words is 12-bits

long and can hold a complete assembly

level instruction, including any data

associated with it. All instructions oper-

ate in a single instruction cycle (except

when the instruction causes a branch

or a jump in the program, in which

case it takes two cycles). An instruc-

tion cycle takes 1μs, so that’s a million

instructions executed every second –

fast enough for the simple functions

that we might put this device to.

The trick with using such a limit-

ed device is applying it to projects

that can accommodate it – if you fi nd

yourself having to add many external

components (or more expensive com-

ponents) to circumvent the processor’s

limitations, then you will probably be

better off choosing a more powerful

processor. We will choose our projects

carefully to be relevant to a processor

of this size.

The next challenge is what can I do

with just 512 program instructions? A

surprising amount, as it turns out. Even

more surprising is that you do not have

to revert to programming the chip in as-

sembly language – we can write in the

‘C’ high-level language in many cases.

There are some subtleties required in

setting up the project code build fi les,

but we will explain these issues and

how to avoid them next month.

Software set-up

If you wish to follow along at home and

build these circuits, you will need to

download the software development

tools from Microchip. We will be using

the MPLAB X IDE, and the MPLAB XC

Compilers. Both of these are provided

for free by Microchip. MPLAB X IDE

can be downloaded from here: http://

bit.ly/pe-may19-mc1

INDF

Data memory Code memory

00h

01h TMR0

02h PCL

03h STATUS

04h FSR

05h OSCCAL

06h GPIO

CMCON0

General-

purpose

registers

07h

08h

1Fh

000h Reset vector

User code space

Oscillator

1FFhcalibration value

1

2

3

4

8

7

6

5

NC

(positive supply) VDD

GP2/T0CKI/FOSC4

GP1/ICSPCLK

GP3MCLR/VPP

VSS (negative supply)

NC

GP0/ICSPDAT

IC1PIC10F202

Fig.2. PIC10F202 memory layout

Fig.3. PIC10F202 pinout