D.1 Formatted IO: (PRINTF, SCANF, SPRINTF, SSCANF)

Microprocessors



char c;

c = 0x41;

printf("%c



%d



A



65



As an

ASCII

character



(a) Some format specifications.

Replace %d with %u for unsigned int

types. Replace %d with %ld for

long types, and %d with %lu for

unsigned long types.



%x", c, c, c);



41



In

decimal



In

hex



printf("A:%10d B:%-10d C:%04x \n",c,c,c);

C:0041



Field width is

10 digits, right

justified



float q;



{



65 B:65



{

{



A:



Field width is

10 digits,

left justified



Field width is 4 characters,

pad with ‘0’ digits

(b) Floating point format specifications



q= 0.001234;



0.001



C:%e\n",q, q, q);



B: 0.001234



Field width is 6 digits, with three

digits to right of decimal point



C:1.234000e-03



{



A:



B: %f



{



printf ("A: %6.3f



{



558



No field width

Scientific notation

or precision specified



char c, buf[20];

c = 0x41;

sprintf(buf,"%c %d %x", c, c, c);



(c) print to an in-memory buffer

after execution, buf contains

A 65 41



FIGURE D.1 printf() examples.



A %c formats an argument as a single ASCII character, %d specifies an ASCII

decimal format, and %x is used to format an ASCII hex number. The field width is

specified as a number before the format character; %10d specifies a field width of 10

digits. Left justification is the default; a negative sign in the field width (e.g., %-10d)

performs right justification. A leading zero can be specified in the field width as in

%04x to pad the number with leading zeros. A leading l (letter l) is used in the format specification if the argument is a long rather than an int (i.e., %ld instead of %d).

A %u can be specified in place of a %d for an unsigned data type. Floating-point

(float or double) format specifications use %f or %e as shown in Figure D.1b. A format specification of the form %n.mf specifies a field width of n digits, with m digits



Appendix D: Notes on the C Language



559



of precision to the right of the decimal point. The %e specification causes the floatingpoint number to be printed in scientific notation. The sprintf() function is used to

print the string to an in-memory buffer; the first argument to sprintf() is the char

buffer for the output string as shown in Figure D.1c.

The scanf() function is used for formatted ASCII input; within the PICC-18 C

compiler environment the scanf() library function calls the getche() function (get

character and echo) to input each ASCII byte. The getche() function is assumed to

echo its character using the putch() function. The scanf() function expects pointers to the variables in the parameter list; hence, the & operator (address-of operator)

is placed in front of any variables that are passed to scanf(). Figure D.2 shows examples of scanf() with %d (decimal), %x (hex), and %f (float) numbers. The leading

0x on the hex number input is optional. The scanf() function skips over any white

space (space characters, tabs, etc.) it encounters when scanning the input for a

match to the format specification. The sscanf() (string scanf()) function can be

used to read values from an in-memory buffer; the first argument to sscanf() is the

char buffer to scan.

unsigned char c;

float q;

printf("Enter decimal number: ");

scanf("%d",&c);

printf("The number is %d\n", c);



Enter decimal number: 49

The number is 49



printf("\nEnter hex number: ");

scanf("%x",&c);

printf("The hex number is %x\n", c);



Enter hex number: 0xEC

The hex number is ec



printf("\nEnter a float number: ");

scanf("%f",&q);

printf("The float number is %f\n",q);



Enter a float number: 1.239202

The float number is 1.239202



FIGURE D.2 scanf() examples.



D.2 FOR C++ PROGRAMMERS

A simple, but common error made by C++ programmers when adjusting to C is

variable declarations. In C++, variable declarations can be placed anywhere within

a function as shown in Listing D.1.



560



Microprocessors



LISTING D.1 C++ Variable declarations.

main() {

// compiled with a C++ compiler

char c;

c = 0x41;

c++;

int i;

i++;



//variable declaration



}



However, in C the second variable declaration int i must either go at the top

of the function with the char c declaration or be enclosed in a block using {} as

shown in Listing D.2. However, be careful—variables declared within a block {} are

not visible to statements outside of that block.

LISTING D.2 C Variable declarations.

main() {

//compiled with C compiler

char c;

c = 0x41;

c++;

{ // be careful, ‘i’ scope is limited to within brackets!

int i;

//variable declaration

i++;

}

}



D.3 FOR NEW PROGRAMMERS

If you don’t have much programming experience, the number of syntax errors reported by the C compiler after compiling your first program may overwhelm you.

A useful tip relevant to almost any programming language is to fix only the first

syntax error; many of the remaining errors are most probably side effects of that

first syntax error. Do not be intimidated by a listing of 100+ errors; concentrate on

fixing the first one and many of the remaining errors will vanish on the next compile.



D.4 FOR EXPERIENCED C PROGRAMMERS

This book’s usage of the C language is kept fairly simple to aid the new C programmer’s understanding of the example programs. If you are comfortable with the C

language, you are encouraged to modify the book’s examples to make use of the

more powerful features of the language. For example, macros can be employed to



Appendix D: Notes on the C Language



561



automatically compute the numbers for the serial port baud rate, I2C bus speed,

timer interrupt periods, and so forth to make the examples independent of a particular FOSC value. In some of the more complex examples, use of struct data

types for related variables may be appropriate.

If you are an experienced C programmer (perhaps from an X86 platform),

there are many shortcuts for certain code segments discussed in book examples. For

example, the code in Chapter 10, “Interrupts and a First Look at Timers,” for placing data into a software FIFO is written as:

head = head + 1;

if (head == BUFMAX) head = 0;

ibuf[head] = RCREG



Here, BUFMAX is a power of 2, and head is a char variable. An experienced C

programmer might write instead:

ibuf[(++head)%BUFMAX] = RCREG;



This works because % is the C modulo operator and BUFMAX is a power of 2,

meaning that it is evenly divisible into 256, which is the number of possible code

values for the head variable. While the number of C statements is reduced from 3 to

1, the amount of assembly code generated is much higher as the modulo operation

requires a division operation, an expensive operation in terms of machine code and

instruction cycles on the PIC18. So, be careful when writing “tight” C code—it

might not translate into “tight” machine code once it is compiled.



This page intentionally left blank



Appendix



E



Suggested Laboratory

Exercises



his appendix contains the laboratory exercises for a semester-length course

taught at Mississippi State University since summer 2004. We first began

teaching a PIC-based introductory microprocessor course in fall 2003 using

the PIC16F873, and switched to the PIC18F242 in summer 2004.



T



E.1 LAB SETUP

Table E.1 lists the lab equipment assumed by these experiments. Each lab station

should have an oscilloscope and a multimeter. In addition, if each student does not

have a portable PC, every lab station must have a desktop PC. Each lab station

should either have a LAN connection or the lab should be wireless enabled.

TABLE E.1 Suggested Lab Equipment

Equipment



Comment



Networked PC



Lab station only needs a LAN connection if student has a

portable PC.



Multimeter



Basic instrumentation.



Oscilloscope



Basic instrumentation.



PICSTART

Programmer



This is used for programming PICs with the serial

bootloader and initial test programs; it can be shared

among multiple stations.



Soldering and wire

wrap tools/supplies



Either soldering or wire wrap is used for external

connectors; multiple stations can share this.



Universal remote control



Used by Experiment 12 for IR waveform decoding.



563



564



Microprocessors



Because a serial bootloader is used to program the PIC18F242 in a majority of

the hardware labs, each PC must either have a serial port or a USB-to-serial port

adapter. The lab also must have some method of programming a PIC18F242 without a serial bootloader; we use a Microchip PICSTART Plus programmer (Appendix F, “The Jolt/Colt Serial Bootloaders”) shared among 10 lab stations. Software

installed on each PC to support the PIC18F242 experiments are MPLAB, the HITECH PICC-18 compiler, and the Jolt/Colt bootloaders (Appendix F). The lab experiments consist of 13 experiments: one digital-logic based, four assembly

language based, and eight hardware based. In the last week of the semester we hold

a lab practicum to evaluate student skills for ABET assessment purposes. The hardware experiments use a parts kit and a prototyping board purchased by each student. Through the eight hardware experiments, a student builds a PIC18F242

system that has an external I2C serial EEPROM, I2C DAC, asynchronous serial interface, a potentiometer, a mini-jack for audio input/output, and an IR receiver.

Wire wrap is used for external connectors like the DB9 required for the serial port;

the lab has wire wrap supplies (tools/wire) shared by the students. The lab also has

a couple of soldering irons for creating reliable connections to external connectors

if students prefer that over wire wrap. Figure E.1 shows a picture of the prototyping

board at the end of the semester after all experiments have been added to the board.



DB9

IR Receiver

MAX202



Fuse

CD4053

7805



10K SIP



Pwr Switch



240Ω SIP



PIC18F242



MAX517



24LC515



Reset sw.



LM386

Crystal

Audio

Mini-jack

Modular Connector

for ICD2 (optional)



FIGURE E.1 Protoboard at semester end.



10K Pot



Pwr Conn



Appendix E: Suggested Laboratory Exercises



565



The parts kit list used during the fall 2004 semester is shown in Figure E.2 along

with supplier part numbers. We purchase the part kits pre-assembled from Electronix Express (www.elexp.com) at a substantially reduced price over what can be ordered by students in single quantities from parts suppliers. The protoboard and

wiring kit are usually purchased in a previous digital logic course. The modular connector was previously included to support in-circuit programming via the Microchip

ICD2 programmer (Appendix F), but this has been dropped and is now optional.



FIGURE E.2 Parts kit list.



Based on MSU experience, the following points are key for a successful lab

course using this approach:



566



Microprocessors



It is best if students have had some previous experience with protoboards before this lab. In the MSU ECE/CSE curriculum, students are required to take a

digital logic course as a prerequisite with the digital lab experience providing

them with some protoboard experience in wiring 74XX logic. This gives them

an introduction to DIP packages, how protoboard wiring works, an introduction to an oscilloscope and a multimeter, and some basic circuit debugging

(which is greatly increased in this course!). A circuits course is not a prerequisite except for circuit fundamentals as presented in a physics course; we have

majors from electrical engineering, computer engineering, computer science,

and software engineering who take this lab so a circuits prerequisite is not possible.

The teaching assistants (TAs) for the lab must be talented, knowledgeable, dedicated, patient, and have had previous microcontroller experience to assist students in the inevitable hardware debugging problems. We recruit our TAs from

the graduates of this course; the first TAs came from a traditional microcontroller course that has since been replaced by our second course in embedded

systems. We limit enrollment in each lab section to 10 students because the

hardware labs dramatically increase the “help me!” load on the TA. The first

two hardware labs are the worst from a TA load perspective when students are

bringing their initial PIC18F242 setup to life; our labs are open so students can

work on their protoboards outside of normal lab hours if needed.

The TA must have a reference board built for demo purposes and for checking

bad part problems by plugging the part into the reference board.

A spare parts supply is an absolute necessity, as students demonstrate an amazing talent for destroying ICs. The TA, course instructor, IEEE/HKN, or some

central shop can sell these. Fuses have been our top sellers.



ON THE CD



It is rewarding to watch students with near-zero prototyping skills gain confidence as the semester progresses, and show pride in their board as they build it up

from a collection of ICs and wires to something that records and plays audio in the

final experiment.

In the following experiment descriptions, the prelab activity should be completed before the student enters the lab. All of the files and zip archives referenced

in the lab descriptions are contained in the code/labs directory on the companion

CD-ROM.



E.2 EXPERIMENT 1: A STORED PROGRAM MACHINE (CHAPTERS 1, 2)

This experiment has the students implement the Number Sequencing Computer

from Chapter 2 using the digital logic simulation package from a previous digital



Appendix E: Suggested Laboratory Exercises



567



logic course. At MSU, this is the Altera Maxplus package. We give the students the

design already entered in Altera Maxplus and have them write a program that outputs their own student ID number or phone number. The ROM module in Altera

MAXPLUS reads its initial contents from an external file; the students must assemble their program and modify the ROM file that specifies the machine code for their

program. Students also step through the logic simulation within Altera MAXPLUS

and determine how many clock cycles it takes to output the two number sequences

based on the LOC input. The nsc.zip archive on the books’s supplemental lab Web

site (www.reesemicro.com) contains the Altera Maxplus design for the number sequencing computer in Chapter 2. In this lab, the TAs also assists the students in installing MPLAB, the Jolt Bootloader, and the PICC18 compiler on their portable PCs.



E.3 EXPERIMENT 2: PIC18XX2 INTRODUCTION (CHAPTER 3)

This experiment introduces the student to the PIC18Fxx2 instructions covered in

Chapter 3 and the MPLAB environment.

Prelab

1. Assemble and simulate the “Simple” example in Listing 3.9 within MPLAB

(filename is mptst.asm). Verify that the final value of k (location 0x02) contains the expected value of 0xC9 when the goto here statement is reached.

2. Change the value of the avalue symbol to be the decimal equivalent of the

last two digits of your student ID. If the last two digits of your student ID

are “00”, use the first two digits. Compute the new expected value of k

when the goto here statement is reached; verify this value by assembling

and simulating the program. Capture a screen shot that shows the program

memory and file register contents when the goto here statement is reached.



Lab Activity

Exploring Data Memory Storage



1. Modify the mptst.asm file so that the CBLOCK starting location is 0x80. Re-assemble and re-execute the program. Verify that the i, j, k variables are updated at locations 0x80-0x82. When the program memory is viewed, the

instruction at program location 0x202 is now different from the original