Microprocessors and
Microcontrollers
Module V
Timer programming
● Two 16-bit timers – Timer 0 and Timer 1
● Each timer accessed as two 8-bit registers
● The timers use 1/12 of crystal frequency regardless of MC
time.
2
TMOD register
3
Gate
● Gate is used to start and stop the timer – through H/W or
S/W
● If gate = 0, S/W control and if gate = 1, H/W control
● In S/W control, TR0 and TR1 bits are set/cleared to
start/stop the respective timer.
4
TCON Register
● TR0, TR1 are used for starting/stopping the timers.
● TF0 , TF1 are timer flags, raised when the count is reached.
5
Timer mode 0 (13-bit mode)
● Lower 5 bits of TLx and 8 bits of THx are used for the
timer.
● When the count rolls over from all 1s to all 0s, TFx flag is
set.
6
Timer modes
● Mode 1 (16-bit mode)
○ Maximum count is 65536
● Mode 2 (8-bit mode)
○ THx is loaded with the 8-bit count and the timer is started.
○ 8051 copies the count to TLx and this acts as the timer.
○ Once the TF flag is set, TLx is automatically reloaded from THx.
○ The programmer need only clear the TF and the timer goes on.
7
Program
Generate a square wave of 50% duty cycle on
P1.5.
clock period = 1.085 µs
No. of counts = FFFFH –FFF2H
= 0DH(13D) + 1 (for roll over)
= 14
Time = 14 X 1.085 µs = 15.19 µs (for half cycle)
For a more accurate calculation, include the clock
cycles for all the instructions in the subroutine. 8
Delay calculation
No. of clocks required = 5 ms / 1.085 µs
= 4608
The counter value = 65536 – 4608
= EE00H
9
Counter programming
● When C/T = 1 in TMOD, it is the counter mode.
● The counter counts the pulses supplied at pins 14 or 15.
10
Program
11
Serial data communication
● Synchronous
○ block of characters
● Asynchronous
○ one byte at a time
○ each character is placed between start and stop bits.
12
SCON register
13
SCON register
● SBUF register
○ 8-bit register used to hold the data for transmission / reception.
14
Baud rate calculation
Timer 1 in
Mode 2 is
used to set
the baud rate
15
Program
16
Program
17
Program
18
Serial port programming in C
19
Interrupts of 8051
● Six interrupts
○ Reset - 0000H
○ INT0 - 0003H
○ Timer 0 - 000BH
○ INT1 - 0013H
○ Timer 1 - 001BH
○ Serial Int - 0023H
20
Interrupt Enable register
21
Enabling/disabling interrupts
or
22
Programming timer interrupts
● Polling the TF wastes CPU time
● TF is raised by means of interrupts
23
Program
24
25
Program
Mode 1 of
Timer 1
26
27
Program
Generate a square wave of 50 Hz on P1.2. Assume XTAL = 11.0592 MHz.. a
28
Programming external hardware interrupts
29
Programming external hardware interrupts
● INT0 and INT1 are low-level triggered interrupts by default.
● Accessed through pins P3.2 and P3.3.
● If interrupts are enabled, 8051 samples the INT pins once
every machine cycle.
● In order to make these edge-triggered, we must set IT0 and
IT1 bits of TCON register.
30
TCON register
31
Programming the serial interrupt
32
Programming the serial interrupt
33
Programming the serial interrupt
34
Programming the serial interrupt
35
Interrupt programming in C
36
Interrupt programming in C
37
Interrupt programming in C
38
Interrupt programming in C
39
Interrupt programming in C
40
Interfacing 8051 with LCD
Pin details
of LCD
Commands
of LCD
41
Interfacing 8051 with LCD
Send a high-to-low
pulse on E for enabling
the LCD
42
Program
43
Program
44
Interfacing 8051 with ADC 0808
● 8051 sends start of
conversion (SOC) signal to
ADC
● ADC returns end of
conversion signal (EOC)
● Input 1 is used for ADC –
hence value of A B C is 001
45
Interfacing 8051 with ADC 0808
46
Interfacing 8051 with ADC 0808
47
Interfacing 8051 with ADC 0808
48
Interfacing 8051 with ADC 0808
49
Interfacing 8051 with DAC 0808
● Digital inputs are converted to
current, which is then
converted into voltage by
connecting a resistor to Iout
pin.
● The total current is a function
of the binary numbers at the
inputs D0 to D7
50
Interfacing 8051 with DAC 0808
Write a program to send data to DAC to generate a stair step ramp
51
Generating a sine wave using DAC 0808
52
Generating a sine wave using DAC 0808
53
