e022014.pdf

MICRO PROCESSOR

PICee

Development System

a PIC16F84-based single-board computer

by Reinhardt Weber, DC5ZM

weber.reinhardt@t-online.de

This single-board computer, using the popular low-cost PIC16F84 micro-

controller, has been developed with educational applications in mind.

The PICee single-board computer

described in this article is a versatile

training and development system

based on the well-known Microchip

PIC16F84 microcontroller. The micro-

controller’s flash memory is electri-

cally erasable: hence the ‘ee’ in the

title. In contrast to the 89C8252

Flash microcontroller board

described in our December 2001

issue, the 16F84 processor used here

is a so-called ‘RISC’ (reduced

instruction set computer) microcon-

troller with only a small number of

instructions. The PICee board allows

experimentation with all 35 of the

processor’s instructions without

additional hardware. The board

encompasses a wide range of appli-

cations, from a simple LED ﬂasher to

an elegant crystal-controlled clock.

The programming

hardware

The socket can accept all

varieties of the Microchip

PIC16F84, with clock

frequencies from 4 to

20 MHz. The clock

can be generated

using a quartz crys-

tal or an RC oscillator.

Switch S2 selects

between the two oscillator types.

Using the slower RC oscillator is par-

ticularly convenient during experi-

mentation or development. The clock

Elektor Electronics

2/2002

MICRO PROCESSOR

IC1

7805

+UB

+5V

9...12V

S10

1N4007

R23

+5V

LCD

CONTRAST

R31

C13

C14

+5V

D 22

10k

a 1

a 2

a 3

a 4

a 5

a 6

a 7

a 8

a 9

470 µ

100n

47 µ

25V

C16

C10

LCD Module

+UB

100n

16V

IC4.B

IC4 = 74HCT125

+5V

1N4148

a10

a11

a12

a13

a14

a15

a16

a17

a18

a19

a20

a21

a22

a23

a24

a25

a26

a27

a28

a29

a30

a31

a32

IC4.D

R24

R30

R35

R34

+5V

10k

470

Ω

LCD

-E

LIGHT

IC4.C

BC547

CLOCK

RA4

10k

R11

470

Ω

RA3

100k

RA2

IC3

+5V

RA1

RA0

IC4.A

10k

IC4

PIC16F84

100n

RB7

DB9

+5V

MCLR

RB6

RB5

R33

3k3

RB4

R14

RB3

D21

RB2

RB1

1N4148

RB 0

CUR LIM

CAT

OSC1

OSC2

IC2

R13

100

TL497

+5V

ANO

C IN

COL OUT

R12

R15

R16

R17

R18

R19

R20

R21

R22

R25

R26

R27

R28

R29

FREQ

INH

R32

R10

SUBS

E OUT

+5V

220p

D 8

D 9

D1 0

D1 1

D 12

D 13

D 14

D1 5

D 16

D 17

D 18

D1 9

D2 0

CLOCK

20MHz

C15

C11

C12

100n

27p

1N4148

47 µ

100n

RESET

16V

LED's

BC547

010062 - 11

Figure 1. The microcontroller training board includes a wide range of peripherals for experimentation.

frequency is continuously variable

via trimmer P1. Diode D2 and resis-

tor R5 ensure that 5 V is fed to the

MCLR input of the microcontroller in

normal operation. Pushbutton S3 can

be used to reset the processor.

If a DC voltage of around 13.5 V is

applied to the MCLR input, the

microcontroller switches into pro-

gramming mode. The programming

voltage is generated on the circuit

board using a TL497 step-up con-

verter (IC2) and enabled using

switch S1, which takes pin 5 of IC2

to ground. LED D21 indicates when

programming mode has been acti-

vated. The board is connected to a

PC over the serial interface via 9-pin

sub-D connector K2. Connection can

be made using a normal RS232 cable

(not a null modem cable) with a 9-

pin D-type plug at the PICee end

and the usual 9-pin D-type socket at

the PC end. Connection should be

made with the unit switched off —

only when the unit is connected

should power be applied and the

programmer software started up.

The two programming signals DATA

and CLOCK are taken via drivers

IC4.C and IC4.D to microcontroller

inputs RB6 and RB7. Driver IC4.B

delivers data read from the micro-

controller back to the interface. Dri-

ver stage IC4.A is used to control the

programming voltage and reset the

microcontroller.

A microcontroller can become the

heart of a microcomputer system

with the addition of peripheral com-

ponents. The circuit board includes

three typical applications that allow

experimentation with the microcon-

troller’s instruction set. These expan-

sion circuits can also be built into

other applications you may develop.

LEDs D8 to D20 indicates the logic values

present on the RA and RB ports of the micro-

controller. These are very helpful when debug-

ging applications at low speed using the RC

oscillator. They can also be used in your ﬁrst

programming exercises: for example, a LED

flasher, running light, bar graph display, or

LED dimmer. The port LEDs can be enabled

or disabled via miniature switch S8.

Switches S5, S6 and S7 form a mini-key-

board. Pressing S6 or S7 produces a logic ‘1’

at port inputs RA1 or RA0, while pressing S7

produces a logic ‘1’ at both inputs, thanks to

the wired-OR configuration around D3 and

D4. It can be determined in software which

button has been pressed. Three buttons can

give rise to a wide range of control possibili-

ties if one button is allocated to a ‘mode’ func-

tion to select a value to be changed, while the

other two are used to adjust the selected

value, up or down. Think of how alarm clocks

or time switches are set, or how car radios

are controlled.

2/2002

Elektor Electronics

MICRO PROCESSOR

R15

R16

R17

R18

R19

R20

R21

R22

R23

R11

D10

D11

D12

C12

D13

D14

R25

R26

R27

R28

D15

R13

D16

R29

R12

R35

D17

R34

D18

D19

D20

R33

S10

R31

D22

D21

Figure 2. The layout of the single-sided printed circuit board for the PICee single-board computer.

When bright light falls on the LEDs, a volt-

age can be developed at the high-impedance

inputs to the microcontroller that can lead to

false readings: for this reason R34

and R35 are fitted across monitor

LEDs D16 and D17 to pull the input

signals down to ground, avoiding

this unwanted effect.

A 2-line by 16-character alphanu-

Elektor Electronics

2/2002

MICRO PROCESSOR

COMPONENTS LIST

Resistors:

R1,R15-R22,R25-R29 = 1k

R2,R24,R34,R35 = 4k Ω 7

R3,R4,R6...R8,R10 = 10k Ω

R5,R12 = 1k

Ω

R9,R11 = 470 Ω

R13 = 12k Ω

R14 = 10

Ω

R23 = 33 Ω

R30 = 470k Ω

R31,R32 = 270

R33 = 3k Ω

P1 = 100k Ω

preset

P2 = 10k

preset

Capacitors:

C1,C2,C3,C5,C6,C7,C10,C11,C12 =

100nF

C4 = 220pF

C8,C9 = 27pF

C13 = 470 µ F 25V radial

C14,C15,C16 = 47

F 16V radial

Semiconductors:

D1 = 1N4007

D2-D7 = 1N4148

D8-D11,D16-D19 = LED, 3mm, yellow,

low current

D12-D18,D20,D21 = LED 3 mm, red, low

current

D22 = LED, 3 mm, green, low current

T1,T2,T3 = BC547

IC1 = 7805

IC2 = TL497AC

IC3 = PIC16F84

IC4 = 74HCT125

Miscellaneous:

K1 = mains adaptor socket, PCB mount

K2 = 9-way sub-D socket (female), angled

pins, PCB mount

K3 = DIN41612 connector, model B (Con-

rad Electronics # 741582)

K4 = 16-way SIL connector*

L1 = 100 µ H

S1,S2,S4,S8,S9,S10 = toggle switch, 1 c/o

contact, or 3-way pinheader with jumper

S3,S5,S6,S7 = pushbutton, e.g.,

ITT/Schadow type D6

X1 = quartz crystal socket with crystal*

Heatsink for IC1, e.g. type ICK35 (Fischer)

(Dau Components)

PCB, order code 010062-1

Disk, contains example programs, order

code 010062-11

meric LCD dot matrix module can be

ﬁtted to allow the system to display

more complex information. This mod-

ule is based around the Hitachi

HD44780 controller, which has

become something of an industry

standard. The display is driven using

the E (enable) and RS (register select)

signals, which are connected to port

pins RA2 and RA3. The read/write

(R/W) input of the module is tied per-

manently to ground (GND), since it is

only rarely that read mode is wanted.

Trimmer P2 allows the display con-

trast to be set, and the backlight can

be turned on and off via switch S4.

The LCD controller can be enabled

and disabled via switch S9.

All the microcontroller pins as

well as the input power supply volt-

age and the regulated 5 V supply are

available on a 32-way DIN41612-

style female connector. Special appli-

cation circuits can be constructed on

low-cost prototyping board and con-

nected to the single-board computer

via a complementary 32-way male

connector.

Power for the single-board com-

puter comes from an external mains

supply connected via low-voltage

connector K1. The input voltage can

be anywhere between 9 V and 12 V.

The built-in fixed voltage regulator

IC1 produces a stabilised 5 V output.

LED D22 indicates when power is

applied. If the input reverse polarity

protection diode D1 and the regula-

tor are dispensed with, battery oper-

ation from four NiCd cells (4.8 V

total) is possible.

Construction of the circuit on the

printed circuit board shown in Fig-

ure 2 should present no problems;

sockets should be used for all ICs and

for the crystal. The circuit board —sur-

prisingly for a single-board computer

— is only single-sided and therefore

inexpensive. The price for this is 18

wire links in the well-spaced layout.

All 13 of the microcontroller’s port pins as

well as the power supply are brought to the

connector in the middle of the circuit board,

next to which, as can be seen from the main

photograph, the LC display is ﬁtted. The elec-

trical connection to the display can be made

2/2002

Elektor Electronics

MICRO PROCESSOR

with a combination of SIL connectors or alter-

natively short wire links can be used. The

switches shown in the circuit diagram can be

replaced with jumpers.

Free programming

software

A wide selection of literature is available on

learning to program the PIC microcontroller

family. A few starting points are given in the

references, and the Internet is also a rich

source of information, with numerous articles

and items of hardware and software avail-

able. Also, almost every technical college will

have some information on their homepage

about the PIC microcontroller: just type

‘PIC16F84’ into your favourite search engine.

You will need some programming tools to

develop assembler programs. The Windows

program MPLAB.EXE (editor, assembler and

simulator) and the DOS programs

MPASM.EXE (assembler) and PSIM.EXE (sim-

ulator) produced by Microchip are recom-

mended. These are freeware and can be

freely downloaded from the Internet.

Datasheets for the microcontroller and numer-

ous example programs are also available.

One example of free programming soft-

ware is NTPicprog , which can be found at

http://home.swipnet.se/~w24528/NTPicprog

( Figure 3 ). ICPROG.EXE, available from

www.ic-prog.com also works well. When set-

ting up the hardware, the PICee system

appears as ‘JDM Programmer’ ( Figure 4 ). The

trusty PIP02 software is also available for

those who would rather work under DOS.

Once the source code for the program

(*.asm) has been prepared and successfully

converted to a *.hex ﬁle using the assembler,

this can be downloaded into the flash pro-

gram memory in the microcontroller.

A large number of example programs can

be found on the project software disk ref.

010062-1 .

Figure 3. The NTPicprog programming software.

Figure 4. Hardware settings using ICPROG.

Relevant Internet sites:

http://www.microchip.com

http://www.wolfgang-kynast.de/pic.htm

http://www.ludwig-geissler-schule.de/docs/picee/picee.html

(010062-1)

References:

Back to school

David Benson

Easy PIC’n

Publisher: Square 1

David Benson

PIC’n up the Pace

Publisher: Square 1

This circuit was developed and tested at the Ludwig-Geissler school in Hanau,

Germany with a particular view towards its use in teaching. The single-board

computer has been used there very successfully for several years in various

classes, both for training in the use of microcontrollers and in project work.

For a component cost of only about thirty pounds, it also offers the radio ama-

teur or electronics hobbyist an ideal platform for experimenting with and

developing ideas.

F. Volpe

PICs in Practice

Publisher: Elektor Electronics (Publishing)

Elektor Electronics

2/2002

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