2015_16 - lecture for rts laboratory 2 (1)

7/25/2019 2015_16 - Lecture for RTS Laboratory 2 (1)

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RTS Laboratory 2Getting to grips with devices, data sheets and

graphics (as an example of a device library)


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Looking at PICs (in general) Getting a working system

Todays material


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PICs (yo will remember) range in cost, si!e,speed and complexity "o pick the chip best sited to the task in hand

#nce yo have decided on yor device thepractical work can begin It may be that yo start with a development board

$nd then move to a bespoke board

#r design the board based on yor analysis of the

task it will be addressing

What does a pic look like


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% pins & PIC'(L)'*+' -ote.

/ome pins have mltiple labels

Some examples of PICs


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To slightly(! more complexo"es


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0here will always be a few common things Power (1dd and 1ss)

Inpt#pt ports $s the chips get 2bigger3 yo get more

4i5erent chips will have di5erent devices integratedinto them It is p to yo, the programmer, to specify what yo

need the pins to do

$ 2reset3 6 7CL8 "o may sacri9ce this is the pin dobles p for a

fnction yo re:ire more

#o$e%er&


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We ca" ha%e circ'its as simpleas

http.circit&!one;comediy


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"or board is a little more complex with anmber of peripherals bilt on the PC@ 0ri&axial $naloge $ccelerometer

/peaker

#LA4 4isplay ('+x? pixels)

$4C

0o make se of these we need to doknow afew things Dnow what is connected to PI-s on the chip

Con9gre the integrated device(s) pins

o'r PIC board


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Ehen working with development boardssch as the ones yo have it is a good ideato look at the schematics for the kit 0his will allow s to see what is bilt in

Fow things are connected

"o can 9nd the schematics in the 2sersgide3 (on moodle) Let s take a look at them and explain how they

describe the board

I"%estigati"g yo'r board


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The )o%er%ie$


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The Peripherals

0hese are links backto the processor


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The a'dio


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sefl as we will be writing code to monitor themH

-ote the names on the

chip 8C 8$% #n the switches note

the line over the name

&J negative logic

*"d o"e more + thes$itches


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Consider the switches, they are linked to 8C (/witch


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0he 9rst task is to indicate how the pin is towork (will it be an inpt or an otpt


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Consider we have P#80$ (an % bit port) andwe wish 8$>,', to be an inpt

$ll other pins (8$'&8$+) to be otpt

Ee create a the binary representation as

/o in binary we need to set the 08I/$ as >b>>>>>''' or >x>+ or +

This is best do"e byexample

R*. R*/ R*0 R*1 R* R*2 R*3 R*4

> > > > > ' ' '

'% ? '? % '


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#ne wold set the register as movlw b3>>>>'''3

movwf 08I/$

-ote. Ee wold not need to de9ne 208I/$3 as the

selection of device wold provide this to thecompiler

0he good news Ee are not sing assemblerH

If 'si"g assembler ($e are"ot!


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0he xc'? compiler 2knows3 abot thevarios devices and pins on the chip via theheader 9le yo inclde (the2devicex>+N

08I/$ M >b>>>>'''N

So ho$ do I do this i" C


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Ee can make se of the portH0he (basic) ports act like memory

$ vale we write to them 2latches3 ntil wechange it

Ee see the vale presented across the (inpt)pins as a vale

/o, if we had set 08I/$ M >b>>>>>>>>N $ll otpt

0hen P#80$ M >b'>'>'>'>N

Latches alternate pins at *v, >v, *v etc; (if1ddM*v)

5"ce co"6g'red +$riti"go't


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Ee can read the vale across the pins and store this ina sitable variable

/o, if we had set 08I/$ M >b''''''''N $ll Inpt (binary notation)

08I/$ M >x5N $ll Inpt (hex notation)

08I/$ M **N $ll Inpt (decimal notation)

0hen Connect *v (1dd) to pins 8$>,',,

Ee wold see this across the port as

>>>>'''' /o if we had (assming 1on$ is an integer)

1on$ M P#80$N

0hen 1on$ wold (if displayed) contain '*

Readi"g i"


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If we wanted to (say) read only one pin wecold 8ead the vale on the port

7ask ot the other bits (se an $-4)

Look at the reslt

0o change the otpt state of one pin 8ead the vale on the port #8 the relevant pin (trn 2on3)

$-4 the relevant pin (trn 2o53)

,'t $hat abo't i"di%id'alpi"s-


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0he pins too have names and we can access these of Port $

Ode9ne P#80$bits;8$>

There is a" easier $ay

@t what are theseK


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"o will remember we had strctres

* remi"der from C

strct 4ata/tct int aN int bN

int cN int dNQN

int main(void)

strct 4ata/tct 4/N 4/;a M 'N 4/;b M N retrn >NQ

In this example we have for

separate variables within thestrctre

0he total si!e of the strctreis that of for integers;

$n integer is (on a PC) bytes so '? bytes in total


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@it9eld strctres. we de9ne variable si!esin terms of bits (integer types #-L")

* "e$ bit of C

strct 4ata/tct int a.'N ' bit (> or ')

int b.N bits (>,',,) int c.N bits (> to +) int d.N bits (>,',,)QNint main(void)


In this example we have forseparate variables, all integers which

we can se as re:ired

0he /A4 si!e of each (and so range)is de9ned by the nmber of @I0/

In this example the 0#0$L 2sed3 si!eis 'RRR M % bits M ' @yte

It will take on the si!e of an integer asthis is 2base3 nit


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@it9eld strctres. we de9ne variable si!esin terms of bits (integer types #-L")

We co'ld 'se a C#*R

strct 4ata/tct char a.'N ' bit (> or ')

char b.N bits (>,',,) char c.N bits (> to +) char d.N bits (>,',,)QNint main(void)


In this example we have forseparate variables, all CF$8s which

we can se as re:ired

0he /A4 si!e of each (and so range)is de9ned by the nmber of @I0/

In this example the 0#0$L 2sed3 si!eis 'RRR M % bits M ' @yte M ' char

It will take on the /$7A si!e of anchar as this is 2base3 nit


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0his is a techni:e in Cwhere we allow variables to/F$8A memory

78I58Snion 4atanion int a,bN Soat c,dNQN

int main(void)

nion 4atanion 4N 4;a M 'N printf (TUn4;a M Vd T, 4;a)N printf (TUn4;b M Vd T, 4;b)N4;b M N

printf (TUn4;a M Vd T, 4;a)N printf (TUn4;b M Vd T, 4;b)N

retrn >NQ

In this example we have

de9ned for separatevariables

0he address of each ishowever the /$7AH I;e; a MM b MM c MM d

Ee change one, we a5ectthe others


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78I58S + i" actio"

nion 4atanion int a,bN Soat c,dNQN

int main(void) nion 4atanion 4N 4;a M 'N printf (TUn4;a M Vd T, 4;a)N printf (TUn4;b M Vd T, 4;b)N

4;b M N printf (TUn4;a M Vd T, 4;a)N printf (TUn4;b M Vd T, 4;b)N

retrn >NQ

#tpt (PC)


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$s yo will remember, we control PICs (andsch devices) by setting register vales; $ register may control a nmber of related

parameters, each perhaps needing a

di5erent nmber of bits0he header for the chip 2de9nes3 each of

these sing the same name Ee then set these vales as re:ired

@0. 0his was we need to set everything in one go

Why is he telli"g 's this-


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Co"sider

0o set this we might se

0'C#- M >b'>'>>>>>''>>''>N0'C#- M >x*>??N0'C#- M >*%N

0o change a bit, we need to 2know3 the crrent state andthen modify as re:ired (sing #8 and W#8 to setclearbits)


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Ee create a @I0IAL4 strctre thatdescribes the register Ee -I#- this 2over3 the register address

0he header 9le de9nes the name for s

The )Cle%er trick

strct nsigned .'N nsigned 0C/.'N nsigned 0/"-C.'N nsigned .'N nsigned 0CDP/.N

nsigned 0G$0A.'N nsigned .?N nsigned 0/I4L.'N nsigned .'N nsigned 0#-.'N QN

Ee can then /et the whole register in one

go

0'C#- M >x*>??N /et -4I1I4$L items as

re:ired 0'C#-bits;0CPD/ M N

0'C#-bits;0#- M >N

0'C#-bits;0#- M 'N


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$s well as basic I# ports, PICs have manyother (often complex) devices 0imers

PE7 modles

$80/ $ll of which we con9gre throgh the se of

registers sing the method detailed todayH

$nd will talk more abot next weekH

9or more complex de%ices


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Ee are often given 2pre&written3 code that provides swith a nmber of fnctions we then make se of

7icrochip provide a large nmber of sch libraries

#ne sch is the graphics library 6 and it is that yo will besing this week

Ehile it 2looks3 complicated if yo read the 'serg'ides o" :oodlein conBnction with the sample

code provided yo will soon get to grips with it

Anabling yo to modify things and so make yor ownapplciation;

9or )%ery complex thi"gs


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0his code has a nmber of samples showinghow the graphics fnctions are called

It incldes 4isplaying text on the screen

/ome simple shapes

/how how the slider can be sed

"or tasks $re to se these to display information on the

screen (nmbers)

0o bild a little 2egg timer3

The sample code


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Ee dig deeper Look how the Check/witch/' fnctions work

Consider techni:es inclding Polling

Interrpts 0imers

$nd (alas) I have to let yo se global variables

@t in a very controlled mannerH

8ext $eek (lect're ; labs!

2015_16 - lecture for rts laboratory 2 (1)

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