2001_02_supp(1).pdf

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JOHN BECKER

HOW TO USE

GRAPHICS LIQUID

CRYSTAL DISPLAYS

WITH PICS

A step-by-step guide to understanding

and using pixel-matrixed graphics l.c.d.s

with your PIC microcontroller projects.

RAPHICS

liquid crystal displays

have been available for several

years. It would appear, though, that

EPE

readers have not successfully

explored them. At least, that seems the log-

ical conclusion since we have never been

offered a design which uses them.

One reason may be that the prices of

such devices have, in many instances, been

somewhat expensive. Whilst many contin-

ue to be pricy for the average hobbyist, less

expensive ones have been making their

appearance.

Possibly the principal reason we have

not been offered working designs is that

readers have not been able to obtain, let

alone interpret, the data sheets associated

with them.

The latter stumbling block very

much faced the author when he

decided that he would like to know

how to use graphics displays.

Intermittently over several days,

he scoured the Internet in search of

their manufacturers and suppliers.

As it turned out, there are quite a

few around the globe, but when it

came to obtaining data sheets –

well, that was a totally different

matter.

intelligibility is also marred by having

been translated by someone inadequately

familiar with English. Gross errors of fact

were spotted as well.

To cut short a lengthy and convoluted

tale, no manufacturer or supplier could be

found who had adequate data for graphics

displays available for download.

Farnell appeared to have a

selection of displays within a rea-

sonable price range, but stated “no

parametric

data

available’’.

Attempting to Net-search for the

manufacturer of these devices,

Perdix, only revealed countless

sites to do with

partridges

(a bird

for which the Latin and Greek

name is

perdix!)

Whilst research had showed that

RS Components supplies graphics

displays, the only data sheet (RS

DATA DENIAL

During the Net searches, however, vari-

ous manufacturers had stated that their dis-

plays were controlled by the Toshiba

T6963C chip, the same device as used by

Powertip. Seemingly, then, the control

architecture offered by the T6963C could

be regarded as an “industry standard’’, and

thus worth pursuing further through a

Powertip display, the PG12864.

Toshiba state that the T6963C is an l.c.d.

controller that has an 8-bit parallel data bus

plus control lines for reading or writing

through a microcontroller interface (such

as a PIC).

It has a 128-word character generator

ROM (read only memory) which can con-

trol an external display RAM (random

access memory) of up to 64 kilo-

bytes. It can be used in text,

graphic and combination text-and-

graphic modes, and includes vari-

ous attribute functions.

Searching Toshiba’s web site,

the T6963C was eventually locat-

(under

Analogue

Peripherals/LCD Driver!), and its

46 page data sheet downloaded.

This data turned out to be the

key to getting to grips with graph-

ics l.c.d.s. Not so much because

the data sheet was intelligible

(which it did not become until

much later), but because it gave

programming examples of con-

trolling the T6963C, albeit written

in a microcontroller command

language unknown to the author.

There were, though, sufficient

commands whose structure

appeared to be close to some other

machine code dialects with which

the author is familiar, for a trans-

Photo 1. Graphics l.c.d. screen showing the display generated

lation to PIC microcontroller

language to be attempted.

by the author’s first demo program.

298-4613) available turned out to be spe-

cific to a development kit which uses them.

However, in the RS catalogue, the man-

ufacturer of their displays is quoted as

Powertip. Doing a Net-search, and eventu-

ally accessing Powertip’s web site in

Taiwan, rudimentary data on the devices

was located. But, frustratingly, Powertip

denies access to its data sheets by those

who are not registered distributors.

Contacting the technical department at

RS, the author was put in touch with an

agent who imports from Powertip. This

company sent Powertip’s data sheet, a doc-

ument which might, perhaps, be under-

standable to those already familiar with

graphics l.c.d.s but is certainly not con-

ducive to teaching those who do not. Its

TOSHIBA T6963C

Everyday Practical Electronics, February 2001

Special Supplement

EE E

FR LE

Photo 2. Toshiba’s demo display.

Success was achieved when the display

in Photo 2 appeared on the author’s

Powertip PG12864 64 × 128 pixel graphics

l.c.d. screen – eventually!

POWERTIP PG12864

Whilst it is the Powertip PG12864 graphics

display (RS 329-0329) used in the demos

discussed, the commands are relevant to

any

connected to a negative voltage supply, of

graphics l.c.d. which uses the Toshiba

about –5V, via a contrast-adjusting preset

T6963C controller, although the pin

potentiometer of typically 10kW to 25kW.

count/order may differ between display types.

A summary of the pin functions is given

The PG12864 has the pinouts shown in Fig.1.

in Table 1.

The PG12864 has a full dot-matrix l.c.d.

Which brings us to the first of the major

structure consisting of a visible screen area

discrepancies found in Powertip’s own data

having 128 dots × 64 dots (8192 dots in

sheet (be warned if you obtain it!):

total). There are eight data lines, D0 to D7,

and six control lines comprising WR, RD,

1. Powertip quote data line D0 as being

CE, CD, RST and FS, names which will be

MSB. It’s not. D0 is LSB (see Table 1).

clarified shortly.

The display has a single positive supply

2. Powertip also show an incorrect cir-

line (Vdd) at pin 3. The recommended

cuit diagram for the control of the screen

working voltage is 5V, with an absolute

contrast. The control pot is shown wrongly

maximum of 7V. There are two 0V con-

connected across pin 3 (+5V) and pin 9

nections, of which GND (pin 2) is the sig-

(RST) with the wiper on pin 4 (CX).

nal ground (Vss), and FG (pin 1) is the

Furthermore, pin 9 is marked as V

(–VE). This configuration does not work.

ground connection for the display’s metal

frame (bezel).

Table 1. Graphics l.c.d. pinout functions.

Display contrast is

controlled via pin 4,

Symbol

Function

named as CX in Fig.1

Frame ground (connected to metal bezel)

but can also be

GND

Signal ground supply (Vss)

referred to as V0.

+5V

Positive supply for logic (Vdd)

This pin is normally

Negative supply (V0) for l.c.d. contrast

(–3·5V approx)

Data write (active low)

Data read (active low)

Chip enable (active low)

CD = 1, WR = 0: command write

CD = 1, WR = 1: command read

CD = 0, WR = 0: data write

CD = 0, WR = 1: data read

Module reset (active low)

Data bus (D0 = LSB, D7 = MSB)

Font select:

FS = 0:

8 × 8 dots font

FS = 1 (or open–circuit): 6 × 8 dots font

10–17

RST

D0–D7

Fig.1. Pinouts of the Powertip PG12864 graphics l.c.d. module.

Fig.2. Circuit diagram for the PIC-

controlled Graphics L.C.D. Demo.

Special Supplement

Everyday Practical Electronics, February 2001

Fig.3. Component and full size copper foil track

master pattern for the Graphics L.C.D. Demo

printed circuit board.

Pin 9 (RST) does not go to –VE. It is

held at logic 1 (+5V) for normal control

chip operation and may be taken (briefly)

to 0V to reset the chip, but it

must never be

taken negative,

nor should one side of the

control pot ever be connected to this pin.

Experimentation showed that the control

pot’s wiper

should

be connected to pin 4.

One outer terminal of the pot then connects

to a negative supply of, for example, –5V.

The unused pot terminal is best connected

to the wiper. This is illustrated in the demo

circuit diagram (Fig.2.). The preset is

adjusted until the desired contrast is

observed.

The Toshiba data sheet does not discuss

l.c.d. contrast setting, whilst that from RS

is highly ambiguous on the subject.

COMPONENTS

Resistors

R3, R4

All 0·25W 5%

VR1

VR2

470W

10k (2 off)

carbon film.

Approx. Cost

Guidance Only

excluding case & batt.

microcontroller,

pre-programmed

(see text)

78L05 +5V 100mA

regulator

7660 negative voltage

converter

min. s.p. push-to-make

switch

3·2768MHz crystal (see

text)

graphics l.c.d. module,

Toshiba T6963C-

based, 64 x 128 pixels,

e.g. Powertip

PG12864-F (see text)

£50

IC2

Potentiometers

See

IC3

22k (or 25k)

min. preset,

round

10k min.

preset, round

page

(see text)

SHOP

TALK

Miscellaneous

DEMO CIRCUIT

Capacitors

10p ceramic, 5mm pitch

(2 off)

C3, C6, C7 22m radial elect. 16V

(3 off)

C4, C5

100n ceramic, 5mm pitch

(2 off)

C1, C2

The circuit diagram which the author

used in his examination of the PG12864

display is shown in Fig.2. The circuit

includes a PIC16F877 microcontroller

(IC1), a crystal (X1) and its two capacitors

(C1, C2), a 5V voltage regulator (IC2), a

negative voltage inverter (IC3) with its two

capacitors (C6, C7), the PG12864 l.c.d.

display (X2) which is connected to the PIC

via connector pins TB1, contrast control-

ling preset (VR1) and switch S1.

Components R1 and D1 are included so

that the PIC may programmed on–board

via connector TB2 and a suitable PIC pro-

grammer, such as the author’s

PIC Toolkit

Mk2

(May–June ’99).

Resistor R2 and l.e.d. D2 were used by

the author when originally translating the

Toshiba demo program, the l.e.d. being set

on or off at strategic points in the develop-

ing software. They have been left in and

Semiconductors

IC1

1N4148 signal diode

red l.e.d. (see text)

PIC16F877

Printed circuit board, available from

the

EPE PCB Service,

code 288; 8-pin

d.i.l. socket; 40-pin d.i.l. socket; terminal

pin header strips and connectors (see

text); 18-way ribbon cable (a few cen-

timetres); p.c.b. supports (4 off); solder,

etc.

may be similarly used by readers when

writing their own software. The control

line is PORTE pin 0 (RE0).

Resistor R4 is included to keep the

l.c.d.’s CE line high when the PIC is being

programmed (so avoiding random displays

appearing on the screen during that

operation).

Resistor R3 biases high open-collector pin

RA4 allowing demo-stepping switch S1 to

operate correctly.

Components VR2 and TB3 are dis-

cussed in a moment.

A d.c. supply of between about 7V and

12V (nominally stated as +9V) can be used

for powering the circuit via the 5V regula-

tor, IC2.

Incidentally, the crystal clock

frequency is not a critical matter and

other frequencies could be used. If a

crystal of greater than 4MHz is used,

though, the PIC’s configuration bit OS1

Everyday Practical Electronics, February 2001

Special Supplement

Fig.4. Character set for the Powertip PG12864 display (note

that the last two lines may differ in some modules).

not included here, but

the pin order and

functions, and the

controlling software

subroutines, are the

same as used in other

recent “normal’’ l.c.d.

projects designed by

the author and pub-

lished in

EPE.

The

connections can be

ascertained by study-

ing any of those. In

Fig.2, the connections

are shown as TB3,

with VR2 as the

contrast control.

program

loaded

into

the

PIC,

GRAPHEPE.OBJ (source code name

GRAPHEPE.ASM). The software is writ-

ten in TASM, but

PIC Toolkit Mk2

can

translate between TASM and MPASM if

the latter is the programming language you

are used to.

Two other program files will be loaded

into the PIC later on.

The software is available free via the

EPE

web site, or on 3·5-inch disk (for

which a nominal handling charge is made)

from the Editorial office. See

Shoptalk

for

details of both matters.

Having loaded the Toshiba demo, the

display shown earlier in Photo 2 should be

seen. It may be necessary for preset VR1 to

be adjusted before the image is clearly

visible.

It is this demo result which is first dis-

cussed before moving on to the author’s

demos, for which various exercises are

suggested at some points.

Photo 3. Demo printed circuit board assembly.

should be set high and OS0 set low (see

later).

For his own demo board, the author in

fact uses a 5MHz crystal, which does frac-

tionally speed up Demo 8.

It may also be worth bearing in mind

that the author’s forthcoming follow–up

constructional article, in which a

PIC16F877 and the same graphics l.c.d. are

used, also requires a 5MHz crystal.

CONSTRUCTION

PRINTED CIRCUIT

BOARD

It is emphasised that unless you have a

PIC programmer, there is no point in build-

ing this design since much of the discus-

sion here concerns experimental software

changes that you are recommended to try.

These changes, once made, need the soft-

ware to be re-assembled and downloaded

to the PIC.

A printed circuit board design and its

component layout are shown in Fig.3. This

board is available from the

EPE PCB

Service,

code 288.

You will observe that the p.c.b. includes

components VR2 and TB3 towards the

right. These are the points at which the

author also included an ordinary alphanu-

meric l.c.d. so that various routines could

be monitored during the development of

the software translation from Toshiba to

PIC.

The holes and tracks have been left

intact so that the p.c.b. could be used as a

future general-purpose development board

with either type of l.c.d., and in conjunc-

tion with a PIC16F877.

A circuit diagram for the second l.c.d. is

It is expected that all who build the cir-

cuit will be sufficiently experienced not to

need constructional advice. It is recom-

mended, though, that sockets are used for

IC1 and IC3, and that pin header strips are

used for the TB1 to TB3 connections.

Ideally, a graphics l.c.d. should be pur-

chased that already has a suitable pin con-

nector wired to it (see this month’s

Shoptalk

page). The connections to the

p.c.b. are in the “natural’’ order of the

PG12864 l.c.d. used (as shown previously

in Fig.1).

DISPLAY STRUCTURE

Before starting to discuss programming

detail, it is necessary to understand the

physical arrangement of the ways in which

data can be shown on the l.c.d. screen.

There are three options, which can be

summarised as:

Alphanumeric text display

using

the built–in character generator (as with

any standard alphanumeric l.c.d.). 128

characters are available, as shown in

Fig.4, and which are called by their own

location numbers. In a very loose sense

they can be regarded as the equivalent of

ASCII characters. The addressing num-

ber order runs from zero to 127. Writing

any of these values to the screen displays

the “text’’ character associated with it.

The characters in lines 7 and 8 may be

slightly different in some variants of the

PG12864 display.

User–defined character generation

and display.

Again this is similar to the

facilities available on standard alphanu-

meric l.c.d.s, but the quantity of characters

that can be simultaneously stored is far

greater, 128 compared to the typical eight.

The addressing order runs from 128 to 255.

Writing any of these values to the screen

displays the character that the user has

created and allocated to the address value.

PIC PROGRAMMING

Having built the board and proved its

workability, three lots of software need to

be programmed into the PIC, one now and

two later.

Before doing so, though, the PIC needs

to be configured with the following set-

tings (which are all

PIC Toolkit Mk2

default settings for a PIC16F877 running at

4MHz):

CP1 CP0 DBG NIL WRT CPD LVP

BOR CP1 CP0 POR WDT OS1 OS0

Note that Logic 1 and Logic 0 in the set-

tings do NOT necessarily mean that the

function is on/off respectively – refer to the

PIC ’87 data sheet if you need to know

more (also see earlier regarding the oscilla-

tor rate).

For the first part of the discussion that

follows, you need the Toshiba demo

Special Supplement

Everyday Practical Electronics, February 2001

CONTROL LINES

Data is written to or read from the l.c.d.

via the eight data lines D0 to D7. Three

control lines are used in most read or write

situations:

CD: selection of data or command

function, 0 = Data, 1 = Command

CE: chip enable, 0 = enabled, 1 = disabled

RD or WR: read or write functions. These

are two separate lines and the relevant one

is taken low to be active, with the other

remaining high.

Fig.5. Pixel, column and row distribution for the graphics l.c.d.

User–defined graphics detail gener-

ation

in which the “character’’ size is one

pixel high by eight pixels wide (i.e. a sin-

gle byte). Any value between zero and 255

can be written to the screen and the setting

of the binary bits that make up that value

determines whether a screen pixel is turned

on or off.

For both character modes, the characters

are all eight pixels high, but the width can

be specified as six or eight pixels. That is,

the character generation (font) can be set

for 6 × 8 or 8 × 8 format.

Line FS controls the font choice, FS = 0

for 8 × 8, FS = 1 for 6 × 8. The pin has an

internal pull–up resistor that holds it high

(FS = 1) and the pin may be left uncon-

nected if the 6 × 8 font is required (also see

later).

In 8 × 8 font mode (FS = 0), the screen

can display 16 characters horizontally and 8

vertically. In 6 × 8 font mode (FS = 1), the

display format is 20 horizontal × 8 vertical

characters. It is conventional to refer to the

character display in terms of lines (horizon-

tal) and columns (vertical). See Fig.5.

For the graphics mode, 64 character

locations can be written to vertically.

Horizontally, the quantity is determined by

the width mode set for the characters, i.e.

20 or 16.

There are two screen memory areas to

which data is written, known as the Text

screen and the Graphics screen. The Text

screen displays the built–in and user-

defined characters. The Graphics screen

displays only graphics data.

The l.c.d. can be programmed to display

Text only, Graphics only, or Text and

Graphics combined.

There are many additional display

attribute features that can be implemented,

such as highlighting, blanking, flashing,

panning etc.

There is lot of information discussed from

hereon, but it is illustrated with working

program examples, and with many points at

which you can experiment with various

commands in the author’s own demos.

As usual with this type of article, the

author tries to lead you carefully from step

to step.

The timing characteristics for the setting

of the data and control lines are shown in

Fig.6 and Table 2.

Since the l.c.d. includes its own

oscillator, the timings shown are indepen-

dent of the clock rate controlling a PIC

microcontroller.

PIC PORT SETTINGS

CONTROL MATTERS

Those of you familiar with alphanumer-

ic (“intelligent’’) l.c.d. displays will be

aware that they can be operated in either 4-

bit or 8-bit data mode. They can also be

controlled by just two control lines, RS

and E, and rely on a predetermined delay

between sending bytes or nibbles of data.

The same is not true of graphics

displays.

Those using the T6963C can

only be operated in 8-bit mode. They use

five control lines and

require status

check routines to be performed before

each action.

Timed delays are not

used, nor can they

used between data

Table 2. Toshiba T6963C Timing Values

transfers.

Item

Symbol

Min

Max

Unit

There are, though,

CDS

100

–

delay requirements

C/D Set-up Time

–

C/D Hold Time

CDH

concerning the order

, t

–

in which the data and

CE, RD,

WR Pulse Width

control lines are taken

–

high or low, a matter

Data Set-Up Time

Data Hold Time

–

which is discussed

Access Time

ACC

–

150

now. Status checking

Output Hold Time

will be examined

Test Conditions: V

= 5·0V ± 10%, V

= 0V, Ta = –20 to 75°C

shortly.

In the demo programs, PIC PORTC is

used for setting the l.c.d. control lines, and

PORTD for the data input/output lines.

Some microcontrollers and micro-

processors have internal registers which

allow the same data port to be used either

for input or for output without the user

having to specify the port’s function, other

than by the

write

read

command.

For example, the required port (e.g. paral-

lel port connector on a PC computer) has

two separate register addresses, one for

inputting data, the other for outputting it.

These would be equated as values at the

head of the program, e.g. OUTPORT =

&H378 (output register), INPORT = &H379

The next several sections of this discus-

sion relate to the T6963C l.c.d. controller,

and how Toshiba’s example programs are

interpreted using the PG12864 graphics

display and a PIC16F877 microcontroller,

resulting in the display shown earlier in

Photo 2.

Following this, the author’s own

examples of PIC-microcontrolling the

l.c.d. in a variety of situations will be

described. In a future issue, this same

graphics l.c.d. will be the display used in

a PIC-controlled audio frequency oscil-

loscope (currently having the working

title of

PIC G-Scope).

COMING NEXT

Fig.6. Timing waveforms for the Toshiba T6963C graphics l.c.d. controller, see also

Table 2.

Everyday Practical Electronics, February 2001

Special Supplement

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