Delays and counter.pptx

Department of Computer Sc. & Engineering
Chandigarh College of Engineering & Technology (CCET -Degree
Wing)
(A Govt. College under Chandigarh UT Administration, Chandigarh)
Sector-26, Chandigarh - 160019
MICROPROCESSOR
CS-304
DELAYS AND COUNTERS

Department of Computer Science & Engineering
Chandigarh College of Engineering & Technology (CCET -Degree Wing)
(A Govt. College under Chandigarh UT Administration, Chandigarh) ,Sector-26, Chandigarh - 160019
Topics We’ll Cover
• Counters and Time Delays
• Hexadecimal Counters
• Modulo Ten Counter
• Generating Pulse Waveform
• Debugging Counters and Time
Delay Programs
CS-604

Introduction
⚫ This chapter deals with designing of counters and time
delays through software programming.
⚫ Counter and time delays are important technique. They
are commonly used in designing of traffic signals,
digital clocks, setting up reasonably accurate timing
between two events.

Counters
⚫ Designing a counter: A counter is
determined by loading an appropriate
count in the register.
⚫ A loop is setup to decrement the count
(down-counter) and increment the count
for (up- counter) when an event occurs.

Time -Delays
⚫ The procedure for designing a time delay is
same as counter.
⚫ A number is loaded in the register, depending
upon the delay required .
⚫ The register is decremented until count is not
equal to zero by setting a loop.
⚫ A conditional jump is executed when the count
is equal to zero.
⚫ The loop causes delay depending upon the
clock period of the system and number of
instructions.

Time Delay Using One Register

Calculating Time Delays
⚫ Assume clock frequency of system =2MHz.
⚫ So Clock period = 0.5 microsecond.
⚫ Time to execute the MVI instructions=
7 x0.5=3.5µs
⚫ Time Delay in loop= (Clock period x Total
T states in loop x initial count in decimal).
⚫ Time delay =(0.5 x 10-6x 14 x 255)=1785µs
+3.5µs.

⚫ T states of JNZ instruction is shown as 10/7.
⚫ JNZ instruction requires 10 T-states when
loop executes.
⚫ JNZ instruction requires 7-states when loop
fails to execute.
⚫ Loop runs for 255 times and at the last cycle
JNZ executes in 7 T states.
So Time Delay = (1788.5-3x0.5) µs
= 1787 µs.

Time Delay Using Register Pair
2384 H=16x16x16x2+16x16x3+16x8+4x1=9092
Total Delay =24 x 9092 x 0.5x10-6
=109 ms

Flowchart for
Hexadecimal
counter

Generating Pulse Waveform
⚫ PROBLEM ANALYSIS
In this problem, the period of the square wave is 500
us•, therefore, the pulse should be on (logic l) for 250
uS and off (logic 0) for the remaining 250 Its. The
alternate pattern of 0/l bits can be provided by
loading the accumulator with the number AAH (1010
1010) and rotating the pattern once through each
delay loop. Bit Do of the output port is used to
provide logic 0 and l; therefore, all other bits can be
masked by ANDing the accumulator with the byte 01
H. The delay of 250 us can be very easily obtained
with an 8-bit delay count and one register.

Pro
gra
m

Program Description
Register D is loaded with the bit pattern AAH (1010 1010), and the bit
pattern is moved into the accumulator. The bit pattern is rotated left once
and saved again in register D. The accumulator contents must be saved
because the accumulator is used later in the program. The next instruction,
ANI, ANDs (A) to mask all but bit Do, as illustrated below.

⚫ Delay Calculations In this problem, the pulse
width is relatively small (250 us); therefore, to
obtain a reasonably accurate output pulse
width, we should account for all the T-states.
The total delay should include the delay in the
loop and the execution time of theinstructions
outside the loop.

1. The number of instructions outside the loop is seven; it includes
six instructions before the loop beginning at the symbol ROTATE
and the last instruction JMP.
Delay outside the Loop: To = 46 T-states x 325 ns — 14.95 us
2. The delay loop includes two instructions (DCR and JNZ) with 14
T-states except for the last cycle, which has II T-states.
Loop Delay: TL = 14 T-states x 325 ns x (Count - l) + 11 T-states x
325 ns
= 4.5 us (Count- l) + 3.575
3. The total delay required is 250 ps. Therefore, the count can be
calculated as follows:
250us - 14.95us +4.5us (Count - 1) + 3.575us
Count =52.410 = 34H

Debugging Counter & Time Delay Programs
⚫ Errors in counting T-states in a delay loop. Typically, the
first instruction—to load a delay register—is mistakenly
included in the loop.
⚫ Errors in recognizing how many times a loop is repeated.
⚫ Failure to convert a delay count from a decimal number
into its hexadecimal equivalent.
⚫ Conversion error in converting a delay count from
decimal to hexadecimal number or vice versa.
⚫ Specifying a wrong Jump location.
⚫ Failure to set a flag, especially with 16-bit
Decrement/lncrement instructions.
⚫ Using a wrong Jump instruction.
⚫ Failure to display either the first or the last count.
⚫ Failure to provide a delay between the last and the last-
but-one count.

THANK YOU!
Any Queries?
CS-604

Delays and counter.pptx

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