Timer Video Lecture - Embedded Systems (Web) - Computer Science Engineering (CSE)

I discuss about timers basically timers
are the peripherals inside the 8:05 on
micronewton not only 8:05 on timers are
peripherals inside many of the
controllers these are the basic
reference and this peripheral is mainly
used in time based applications so let
us see what are these timers and how how
you are going to use these timers in
case of firm 8:05 on controllers now
basically a timer peripheral contains
some registers and those are called as
timer registers and this timer works
with as it is a register so definitely a
register will be performing any
operation when it is going to receive
the clock signal so here the same thing
timers will be receiving the clock
signal from the crystal oscillator
through some circuit will see what is
itself.you and so it will be reaching
the clock signal okay I am these are
16-bit registers this timer server
16-bit registers and there are totally
two timers are present inside this 8 0
Phi 1 and those timers are called as
timer 0 and timer 1 and both of these
timer 0 and time are one registers our
16-bit registers ok now here these
timers are mainly used for for these
these functions like we can generate the
delay with the help of these timers and
we can count the events which are
happening outside the controller with
the help of these counters and we can
also generate the board rates and this
this functionality is used in case of
serial communication so these are the
three important functions which can be
done with the help of timers now here if
you are generating the delay then that
particular application or functionality
he is named as time okay don't get
confused with the time of peripheral and
time of functionality ok so if you are
generating the delay then that
functionality or application is called
as timer and if you are counting the
events then it is called as a counter
and baud rate generator when if when we
are using it for the third
sláinte that is generating borders for
the serial port okay so these are the
three things that we can do with the
help of this time words in 8:05 or
microcontroller okay and there are two
timers timer zero and then timer one and
the both of these are extreme bit
registers okay see if you are if I'm
using the timer register here X
indicates either 0 or 1
as I told you that there are totally two
timer registers so if if one of the
timer register or if any of the timer
register is used as timer then it is
going to get the clock signal from the
crystal oscillator that is 11.0 fine and
- and this frequency is given as an
input to one circuit that is divided by
two earth why because one machine cycle
is nothing but twelve clock cycles
therefore this this circuit is called as
divided by 2l circuitry to which we are
going to give the input as in 1.0 fine
and - and then the output of this
particular circuit will be given as an
input to this times clock input to these
times okay and this frequency is nine
21.6 clothes
therefore these timers are going to
receive the clock frequency of nine
twenty one point six kilo hertz okay now
here it is going to count the internal
clock pulses okay if I am using it as a
time or then it is going to count the
internal provinces now if I am using the
same time of peripheral as counter then
timer to 0 will be receiving the clock
signal from p0 pin which we have already
seen okay and timer one will be
receiving the clock signal from the
timer one pin that is t1 pin therefore
here these timer registers are now going
to count the external clock pulses which
are given through p0 and then T 1 things
as material okay so if it is a timer
then it counts the internal clock pulses
if it is a if it is working as counter
then it counts the external clock pulses
okay now these are all the registers
which are related to the timer
peripheral and if I want to use this
peripheral then I have to access all
these registers okay now here timer 0
as well as timer1 registers are divided
or are divided into two parts one is tl0
and th0 for timer0 and TL 1 and th one
for time upon ok lower byte L indicates
lower byte and Hetch indicates higher
mind as this 8:05 on ES and 8-bit
microcontroller so it cannot access or
it cannot address a 16-bit register that
is why it is divided into two parts that
is a lower byte and then higher back so
as time or zero is a 16-bit register so
it has two parts one is TL 0 and the
other one is th 0 and as timer 1 is also
16-bit register it has two parts timer
that is a lower byte one time on TL one
and then th one talking so these are the
registers which are basically used for
holding the values okay as soon as we
start the timer
then these registers will be holding the
value it means it means the number of
clock pulses that is resolved by the
timer will be indicated by these
registers okay and then econ is nothing
but a timer control register as this is
a peripheral so every peripheral will
have a control register which is
basically used for controlling the
functionality of that peripheral so with
the help of this control register will
control the functionality of the timers
and then T mode is a register which is
basically used for selecting the mode
and operation of the time okay so let us
see these registers one by one
initially we'll start with T mode
register okay so T mode is an 8 bit
register and here you can see these four
first four bits that is from 7 to 4 that
is MSB four bits or higher legal of this
team order distr are our four timer one
and then the lower four bits are for
timer 0 so if we program these four bits
if you program the higher nibble then
that gets affected to timer 1 and if you
program the lower nibble then that gets
affected to timer 0 okay now let us see
what is the functionality of each and
every bit ok so here this gate and all
these four bits are similar to these
four
but these are used for timer one and
these are useful timer zero okay let us
see the functionality or importance of
each and every bit so gate bit here if
this gate bit is zero then it means that
we are using software control it means
we are controlling the timer with the
help of software that means I am
software is nothing but instructions so
with the help of instructions and
controlling the timer okay
if this is an Hardware that is if it is
programmed to 1 then it means I am just
controlling the time of the help of some
hardware ok it means I have to use
instructions along with the instructions
I have to generate an interrupt signal
then only the timer gets started okay so
here software is nothing but in the help
of instructions and hardware is nothing
but with the help of an instruction
along with and a hardware interrupt
signal okay and see by toolbar here as I
told you that I can use this timer
peripheral to access timer or is
practice counter okay so I have to
mention I have to tell the controller
before using this peripheral that
whether I am using it as timer or else
and using it as counter if I am using
these peripheral as timer then this
particular bit should be programmed to
logic 0 if I am using this particular
peripheral as counter then this
particular bit should be programmable to
logic 1 ok then we have more bits that
is M 1 and M 0 these are called as mode
bits and here we have as you have two
bits here therefore you will get four
combinations that is 0 0 0 1 1 0 & 1 so
0 0 is called as threading bit timer
mode 0 1 is called as 16 bit timer mode
and 1 0 is called as 8-bit auto reload
mode and 1 1 is called as split Kangnam
okay so we'll see all these modes in the
later slides now we have one more
register that is t-con resistance timer
controlling system fit is again of 8
bits ok and here lower nibble lower
nibble of this t-con registers is
related to the interrupts okay and this
higher nibble of click on register is
related to this timers okay so we'll
discuss about this lower level when we
come across the interrupts so
we'll concentrate now on this higher
level so here T f1 which is nothing but
timer one overflow flag okay and TR one
timer one run control bit T of zero time
word zero over flag bit and then TR 0
time at zero for uncontrolled it so with
the help of this overflow flags it is
going to represent the off low status of
the timers what do you mean by overflow
if I have a 4-bit cont 4-bit counter
assume that I have a 4-bit counter now
it starts counting from zero zero zero
zero and it it reaches as soon as it
reaches its maximum value that is 1 1 1
1 then after receiving one more clock
pulse now this counter will be again
initialize it to zero or fill again
starts its count from zero so whenever
this particular condition happens that
is from four ones to four zeroes then
that condition is called as overflow ok
so whenever overflow occurs that has the
time or one or time or zero then these
two bits will become one if it is timer
1 then in this TF 1 will become 1 if it
is timer 0 then P of 0 will become 1
okay now after initializing the timer
after initializing the timer then we
have to start the timer talking so that
is done with the help of this TR mix ok
TR 0 is used for start or stop of a
timer ty 1 0 and the TI 1 is used for
starting or stopping of her time on 1
okay for example if I have a digital
watch so after initializing the distal
watch I need to press the start button
which is provided for the distal watch
then only the clock runs then only the
timer runs so here the same thing is
done with the help of these bills okay
so after initializing the timer you have
to you have to program these bits for
starting the timer as well as for
stopping the time ok if it is programmer
250 if any of these bits are programmer
to 1 then the respect to time or get
started if any of these bits are
programmable to zeros in the respect to
time or gets stopped okay and P of n T
or T of 0 and D of 1 are used for
indicating lis or flow status okay
now this is how the hard way which is
present inside the controller for the
timers okay now let us see how this
Hardware works okay so we have a C by T
bar bit okay and here you can see that
oscillator frequency 11.0 fine and - is
is given to one circuit that is divided
by twelve and the output is given to
timer okay and we we are also getting
that is time and also getting the clock
signal from the other source that is T 1
or T 0 input pin okay if this C by T bar
bit is 0 then it would be working as
timer
therefore this which will be connected
to this point therefore this timer
registers are going to get the clock
signal from the oscillator frequency
from this source okay now if this C by T
bar is 1 then it would be working as
counter therefore this particular switch
will be connected to this point and then
it is it is going to receive the clock
signal from the T 1 or T 0 input pin
that depends on the timer which we are
using okay so if it is getting the clock
signal then only the timer starts
running okay if not it would be stopped
okay now this is up to this part now let
us see what is this so here gate bit
which is going to indicate whether you
are controlling the time of the help of
software or is it the help of hardware
if this gate bit is 0 it means we are
controlling the timer with the help of
software so assuming that this bit is 0
okay now here the output of the nor gate
is 1 so as one of the input to the or
gate is 1 it will not depend on the
other important of these other input is
hardware input therefore it will not be
depending on the hardware input
therefore the output would become 1 okay
now as one of the input to the and gate
is 1 now it would be waiting for the
other input what is the other input that
other input is coming from PR 1 or PR 0
bit in T con okay this is used for
starting or stopping the timer if you
want to start the timer
then the respect to bit that is tr 1 or
TR 0 should be programmable to 1
therefore 1 and 1 to the input of and
gate so the output would be 1 therefore
this
let's toast now as soon as this switch
is closed then the timer register is
going to get the clock signal either
from this source or is from this source
okay now assuming that this TR TR bit is
zero okay as you netic TR bt zero and
here this gate with is zero therefore
the output of the nor gate is one and as
one of the input to the or gate is one
therefore the output of or gate is one
as this TR bit is zero therefore the
output of this and gate is 0 so this
switch will be open it will not be
connected to this particular point as
this switch is not connected to this
point therefore the timer is not going
to get any clock signal so it will not
be it will not be counting the clock
pulses okay so in order to run the timer
definitely you have to give the clock
signal okay now let us see the hardware
control so if this gate bit is 1 it
means we are using in hardware control
therefore the output of this nor gate is
0 numb so as one of the input to the or
gate is 0 then it would be waiting for
the other input now what is the other
input so that depends on this int 1 bar
and d0 one so if you are generating any
hardware interrupt then the output of
this particular or gate will become 1
okay now this TR bit is 1 therefore the
output is of this and gate is 1 and this
which gets closed
if this TR bit is 0 then the output of
this and gate is 0 therefore the switch
will be open ok so this is how the hard
way which is present inside the 8:05 1/4
timers will be working for working for
timers to act as counter are else to
audience to act as time ok now let us
see how these registers are present
inside the modes that is mode 0 more one
more one more 3 so here mode 0 is called
as 13 bit mode why because we are using
only 13 bits of the timer resistor it
might be time or 0 or timer one resistor
ok as you can see here the lower byte of
timer register will be using only 5 bits
and the higher byte of timer register
will be using 8 bits so a complete of 8
plus y is nothing but 13 bits so
here we are using a complete of cutting
bits so that is why it is called us
cutting the timer mode okay now as soon
as when this particular timer registers
gets an overflow condition then this T
of bit will become one which generates
an interrupt okay now here the minimum
value that these time registers are
going to hold is zero zero zero zero
which is represented in hexadecimal
format and the maximum value would be
one triple F H okay
now let us see more one here we have
again TL and pH where X represents
either 0 or else one that depends on the
timer which we are using as we are using
a complete of 8 bits or 16 bits then
that is what is called as 16 bit timer
here the initial value is for 0 set and
the maximum value is for 4x hatch ok as
you can see here TL using 8 bits and th
is also using 8 bits whenever this
particular registers comes across the
overflow that is whenever there is a
transition from this maximum value to
the minimum value then this TF will
become 1 which will generate an inter
and the maximum amount of delay that we
can generate with the help of this mode
1 would be 17 milliseconds we'll see how
to calculate that delay in the latest
lights and we have one more mode that is
more - and it is called as Auto reload
and it is an 8-bit mode why because here
we are using only the 8 bits of TL
register ok so we have to initialize
this TL register with some value and th
register should be in initialized with
an auto reload value so assuming that
this TL is started with 0 therefore for
every clock pulse that this timer
register is receiving it gets
incremented by 1 and reaches to its
maximum value so after reaching its
maximum value FF now if one more clock
pulse is issued by this TLX register
then it would be initialized to the
value which is loaded in this th
register so that is why it is called as
Auto reload mode and for every for every
roll back condition or for every
overflow condition this TF will become
one which generates an interrupted so
that is why it is called as 8-bit Auto
reload why because after ffs this TL
register gets loaded with the
which is present inside this pH register
now let us see the third mode that is
mode 3 now this is called a split timer
why because the timer 0 is divided into
two timers basically we have timer 0
original timer 0 and original timer 1
registers but now in this case timer to
0 will be acting as the two timers that
is TL 0 will be acting as timer 0 and T
H 0 will be acting as timer 1 and we
have one more original timer 1 which is
of 16-bit register ok so in this mode we
can use a total of three times that is
TL 0 as a separate time th 0 as a
separate timer and timer 1 as a separate
timer
ok so I am calling here time PL 0 is
timer 0 why because all the control bits
which are related to TL 0 or timer 0 are
are are used by this PL 0 and all the
control bits which are used by this
timer 1 are now used for this pH 0 so
that is why it is stated as timer 1 and
it is treated as timer 0 and we have one
original timer one resistor and it does
not have any control tips okay
now as you can see here if this PL 0
exceeds its 8-bit maximum value that is
from FF 2 0 0 then this T of 0 will
become 1 indicating that an overflow is
occurred with respect to time or 0 and
here timer 0 is nothing but TL 0 and in
the same way pH 0 if if if it comes
across the overflow condition then this
T of 1 will become 1 indicating and in
turn or generates an Internet ok so
again here TF 1 has become 1 just
because of pH 0 why because it is now
treated as time on 1 and there are no
control bits that are used for this
timer 1 okay there is no TR bit for
timer 1 and there is no PF bit worth
this particular original timer 1 and
this mode is basically used in whenever
we want 3 times whenever we want 3
timers that is I for example I want one
timer for generating the belief one
timer for counting the image
and one timeout for generating the board
rate then I am going to use this kind of
mode and mode two is basically used for
basically used in or that is a serial
communication for generating the models
now let us see how to calculate the time
delay so here for example if I want to
generate a time delay of 10 microseconds
or one millisecond then what I have to
do what are the values that should be
initialized into the timer registers
okay so that is done by following this
particular process okay let us see here
the initial step that we have to do is
we have to divide the required time
delay by one point zero eight four
microseconds so here we got one point
zero eight four microseconds from this
that is eleven point zero five nine two
is divided by twelve therefore 921
cloades so I have to calculate the time
period for this that is inverse of this
frequencies one point zero eight file my
questions therefore for every one point
zero eight four microseconds this timer
register gets incremented by one when it
is received o'clock from the 11.0 fine
into croc source okay so here we have to
divide the required time delay by this
one point zero eight four microseconds
then you will be getting a value now
Here I am representing it with N and it
is in decimal okay now I have to I have
to subtract this decimal value from the
maximum value of time of less than what
is the maximum value of a timer
now here the maximum value of timer will
be depending on the mode of operation if
I am using in more zero then the maximum
value of timer would become one triple F
plus one that we have to calculate in
decimal okay and if it is more one then
the maximum value will become four FS
plus 1 which is nothing but in decimal 6
5 5 3 6 okay so we have to subtract this
decimal value from this maximum value of
primer which should be represented again
in decimal then we'll get the resentment
resultant value in decimal now we have
to convert this decimal value into
hexadecimal why because controller
understands hexadecimal value therefore
convert this decimal result into
hexadecimal then you will get four digit
hexadecimal value
now this four digit hexadecimal value
should be loaded into pH as well as into
TL okay it might be th zero TL 0 or th
one or TL one why because that depends
only on the time of which the user is
using okay so this is how we are going
to generate the time delay by using the
primers thank you
in the next session we'll discuss about
serial communication
you