ITU Control & Automation Eng. Dept.

KON$309$E Microcontroller Systems

Experiment $4$: ADC and USART

Construct the circuit as shown in the Figure.

Check your wiring and make sure that

no connection is made to the $5$V supply.

$$The ADC peripheral should be configured to

sample CH$0$ and CH$1$ using Sequence A$.$

$$The serial port USART$0$ should be configured

for a baud rate of $38400$ and as a serial

terminal.

Write a program that will do the following

in the main loop:

$1.$ Prints out a message such as: "Press a key to start conversion."

$2.$ Starts the ADC Sequence A when a key is pressed from the PC keyboard

$3.$ Waits until one conversion on Sequence A is complete.

$4.$ Converts the results to voltages on the two channels using the reference

voltage of $3$V$3.($Determine the resolution of the ADC by consulting the reference

manual. Use an int$16\_$t$,$ and represent the voltage in millivolts, as the terminal

program cannot print floating point numbers.$)$

$5.$ Prints out the result of the conversion in the format :

"ADC$0=$xxxx mV$,$ ADC$1=$yyyy mV$"$

$6.$ Repeat.

Remember that the terminal program in the PC must also be set to the same

baud rate as Alakart. Otherwise, garbled output, or even, no output will be

seen.

Aim: Using the USART to report periodic analog voltage samples to the PC$.$

In this experiment, we will take sequence samples from the analog to digital

converter on two channels, and report the values back to the PC

For this experiment, you will need to consult the usual reference documents:

$$ LPC$824$ user manual

$$ LPC$82$x datasheet

$$ Alakart schematic diagram

Write the code using the peripheral support libraries $($Xpressso SDK$)$ or direct

register programming or a combination of both.

PART I

Write in your report:

$$What values must be written to which registers so that ADC Sequence A

can be configured to sample CH$0$ and CH$1.$

$$How the serial port is set to $38400$ Baud.

$$The frequencies of "main clock" and "system clock" by checking the

configuration functions. Write which functions you check and how you find

the result.

Store the code for this part in a folder named $"$EX$4\_$PART$1".$

In PART I, we built an analog to digital converter that samples Sequence A once

when a key is pressed on your keyboard. In PART II$,$ we will make the sampling

triggered by the SCT$0$ timer peripheral, in hardware and get the result using an

INT. This is typically how it is implemented in consumer products.

Keep the same circuit as in PART I but add a LED to a suitable PIO$0$ pin with a

resistor. This time the following peripherals must be set:

$$ADC as in PART I with "Sequence A$"$ set to sample ADC$0$ and ADC$1.$

However, the ADC must be configured to be triggered from SCT$0,$ OUT $3$

$$Serial port USART$0$ terminal as in PART I, but with Baud rate $57600$ Baud.

$$SCT$0$ set as an event generator and its output $3$ changes at end of count

event. The duration of SCT$0$ must be calculated and set so that the ADC is

triggered every $500$ms$.$ Remember that system clock is configured to

$24$MHz in the projects provided with the serial port examples and not

$30$MHz$.$

$"$ADC conversion complete" INT is enabled and configured.

$$PIO$0$ is configured such that the pin where the LED is connected is an

output and the LED is turned OFF.

Write a program that will do the following:

$1.$ADC Sequence A is triggered for conversion by the SCT$0$ timer every

$500$ms $($for $2$ conversion sequences $/$ second$).$

$2.$At the completion of the ADC sequence, an end of conversion INT is

triggered.

$3.$Within the ISR: ADC results are stored in a structure, a global volatile

variable is set to True and the LED is toggled.

$4.$Within the main loop of the program: The global variable is repetitively

queried $($checked$)$ to see if it has been set to True by the ISR. If it has been

set to True, then: The ADC results are converted to actual voltages in mV$,$

PART II

and printed in the same format as in PART I, and $($very important!:$)$ the

global variable is set back to False.

As a result, when the program is ran, we should see the LED flashing at $1$s$,$ and

the result of the conversion appears on the screen in millivots every $500$ms$.$

Note that the conversion result is retrieved from the ADC within the ISR, but it is

printed out in the main loop. The ISR must signal the main loop that the

conversion is complete using a global variable that is called a "flag".

Use a chronometer to check that you really get the correct timing. $($Time $20$

blinks and make sure it is close to $20$s$)$

Write in your report:

$1.$ How the SCT$0$ is configured so that it can trigger the ADC every $500$ms$.$

Provide the equation for the calculation by consulting the reference manual.

What values must be written to which registers?

$2.$ Where is the INT vector defined? $($Write the name of the file and copy the line

where it is defined, to your report$)$

$3.$ Describe your program and show how each software function and hardware

peripheral interacts with the others.

Store the code for this part in a folder named $"$EX$4\_$PART$2".$

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