Experiment 3

EE306 Digital Electronic Dsign and Lab

Dept. of Electrical Engineering, KAIST 1

Exp 3. Digital Design Using Microcontroller (1st week)

1. Object - Digital design experiment using 8051 microcontroller. - In this assignment, we are going to design our own digital system to improve our design ability. - Understanding the interrupt operation of 8051 microcontroller. - Getting familiar with COMPACT51 / KEIL uVIsionII development environment for 8051 microcontroller.

2. Problem statement

- Learn how to use 8051 microcontroller-based COMPACT51 board - Learn how to generate 8051-based binary codes using KEIL uVisionII compiler. - Design and implement stopwatch with this board.

3. Background

1) Experiment Environment Composition - Connect COMPACT51 board with PC (using UART Cable) - Setup KEIL uVisionII Compiler to generate 8051-based binary codes ※ If you set up the evaluation version, the maximum file size generated from the

compiler is limited to 2KB. The following explanation is about uVisionII V2.40a evaluation version.

2) How to use KEIL uVisionII (1) Create a new project (Project – New Project..)



- Select the type of microcontroller. In this assignment, select the 8031AH of Intel which is same as the experiment board.

- If you select “Yes” in the following question, STARTUP.A51 file is automatically added to the current Source Group.

(2) Modify STARTUP.A51 - Open STARTUP.A51 file in the Project Workspace.



- Modify following parts in STARTUP.A51 file.

(Before modification) -------------------------------------------------------------------- CSEG AT 0 -------------------------------------------------------------------- (After modification) -------------------------------------------------------------------- CSEG AT 5000H --------------------------------------------------------------------

(3) Add C file - Generate C file (main.c) which will be added to the current Source Group and compiled. - Copy following 3 files and paste to the created project folder CLCD.c, CMPT51.h, init.ini - Click ‘Source Group 1’ in the Project Workspace using a right button of mouse include the appropriate files (CLCD.c, main.c) to the Source Group.

(4) Set up the ‘option’ - Open the ‘options’ in the Project Workspace by click ‘Target 1’ (Right button of the

mouse)



- Open the ‘Target’ tap. Select ‘Memory Model’, ‘Code Rom Size’. Set up ‘off-chip code memory’, ‘off-chip xdata memory’ as follows.

ROM0000H

4000HROM data

5000H

CODE mem

B000HXDATA mem

C000H

When you set up as above, the whole memory map becomes as above figure. ROM will occupy 0000H ~ 4000H, and 4000H ~ 5000H (exactly, 4000H ~ 4100H) is used for data



storage of monitor program in the ROM. 5000H ~ B000H is used for code memory, and B000H ~ C000H is used for data memory. In this manner, since codes are placed beyond 5000H address, we modified STARTUP.A51 file previously.

- Open ‘C51’ tap. Set up 'Interrupt vectors at address' as follows.

8051 defines the interrupt vector as the jump-to address when each interrupt occurs as shown in the following table: between 0000H ~ 0023H. But in case of our experiment board, this address is defined as a part of ROM and you cannot write onto the ROM section. Therefore, the interrupt service routine in these address region need to be moved to some other place. Our experiment boards use ‘double vectoring’ to solve this problem. There are already

‘LJMP’ instruction which changes the interrupt vector into ‘corresponding address + 5000H’ so that they use the address 5000H ~ 502BH when each interrupt occurs. So we have to modify the interrupt vectors accordingly. By doing the above set-up, interrupt service routines that we generate are placed at the location ‘original interrupt vector + 5000H’ (If you want to know more detail, then refer to the references.)

Interrupt No. Interrupt Type Interrupt Vector (A)Modified Interrupt Vector

(A+5000H) - Reset 0x0000 - 0 External Interrupt 0 0x0003 0x5003 1 Timer/Counter 0 0x000B 0x500B 2 External Interrupt 1 0x0013 0x5013 3 Timer/Counter 1 0x001B 0x501B 4 UART 0x0023 0x5023

- Open the ‘Debug’ tap. Select ‘USE KEIL Monitor-51 Driver’ instead of ‘Use Simulator’ and set the initialization File as init.ini



- Click the settings button and check the Serial interrupt as follows

(5) Compile Now, Click ‘Project->Build All Target Files’ to generate binary codes.

(6) Load the program - Click ‘Debug -> Start/Stop Debug Session’. Then binary codes are transmitted through UART cable to the CODE segment section (5000H ~ B000H) of RAM in experiment boards.



Register information and Assembly Code information which is placed at each memory address is indicated as follows. Current yellow arrow indicates 0x0000, where the first instruction of monitoring program in the ROM resides.

- Click ‘Debug->go’, then the monitoring program is started from the current address 0x0000, and stopped at 0x5000, i.e. where the downloaded binary codes are placed.



- And click ‘Debug go’ again, then the downloaded binary codes is executed. At this time, you can perform debugging by using several functions of uVisionII.

3) REG51.H There are several SFRs (Special Function Registers) at 80H ~ FFH in the 8051 microcontroller, and we can control the operation of the processor by using these registers. Since it is troublesome to find or memorize the addresses of registers every time, we try to access the SFR, we use the header file (reg51.h) which includes the macro of register addresses and available bit addresses. You can find more detail information about SFRs in the references, and you can find reg51.h in the directory of KEIL compiler (C:\Program Files\keil\C51\INC).

4) COMP51.H

This file is provided by manufacturers to define the addresses of peripheral devices, contents of board status registers, and LCD-related function to help easily use the board. Before using these macros, it is more important to understand the meaning of each macro by using circuit diagrams of the board.

5) Timer / Counter There are two timers named Timer0 and Timer1 in the 8051 microcontroller which will be used. The registers that control timers are TMOD and TCON, and each bit of registers is



assigned as follows. You can find the meaning of each bit and timer operation in the 8051 User's manual.

(MSB) (LSB)

TCON(Timer Control) TF1 TR1 TF0 TR0 IE1 IT1 IE0 IT0 TMOD(T/CModeControl) GATE C/T M1 M0 GATE C/T M1 M0

Timer 1 Timer 0

16-bit counter 1 TH1 (8 bits) TL1 (8 bits)16-bit counter 0 TH0 (8 bits) TL0 (8 bits)

※ Upper 3 bits can be ignored according to the mode.

TCON register and each symbol of 16bit counter are defined in reg51.h file, so you can use the name when you want to write or read a value to the bit of the register. (For example, TR0 = 0, TL0 = 0x66) This timer supports four modes. You can find the property of each mode in the 8051 User's manual. When you drive the timer using TCON register, it increases the counter value at every input clock from the above 16 bit value. When the counter value becomes 65536 so that overflow occurs, timer interrupt is generated. Timer input clock can be obtained as (system clock/12) or from external input, according to the C/T bit of TMOD register. If (system clock/12) is selected as input clock, since system clock is 11.0592MHz, timer input clock will be 0.9216MHz. If you want to generate timer interrupt every 1ms in this case for example, you can set up the starting value of the timer to (65536 - 922) = 64614. 6) Interrupt (1) What is interrupt? Generally, ‘interrupt’ is defined as the event which changes the operation sequence of the processor. Assuming that, a process reads some sectors of the disk. The process transmits the READ instruction to the disk, and the disk reads the corresponding sector and put them to the sector buffer of the disk. And then the disk sends the interrupt signal to the host. The host which receives the interrupt signals of the disk stops the current operation for a while, and performs the read operation from the sector buffer of disk. For this event, if there is no concept of interrupt, then the host has to poll the status of the

disk often enough since it cannot predict when the disk finishes the operation. However, due to the interrupt signal, the host can perform other instructions after transmitting the READ instruction to the disk.

Mode detailed explanation is available in the textbooks on operating systems.

(2) Interrupt control register (MSB) (LSB)

IE(Interrupt Enable) EA - - ES ET1 EX1 ET0 EX0 IP(Interrupt Priority) - - - PS PT1 PX1 PT0 PX0



There are interrupt control registers as above in 8051 microcontroller. You can find the meaning of each bit in the 8051 user’s manual.

(3) Interrupt type, interrupt vector, and interrupt handler of 8051

Interrupt No. Interrupt type Interrupt vector Modified Interrupt vector - RESET 0000H - 0 Ext. Interrupt 0 0003H 5003H 1 Timer/Counter 0 000BH 500BH 2 Ext. Interrupt 1 0013H 5013H 3 Timer/Counter 1 001BH 501BH 4 Serial Interrupt 0023H 5023H

8051 microcontroller supports 5 interrupts as shown in the above table. For each interrupt vector address, there is an interrupt handler routine to handle the interrupt. When you write interrupt handler using C language as below, KEIL C51 compiler will compile and place the corresponding interrupt vector address. (Following exampling is about Timer0 interrupt (Interrupt No. 1))

-------------------------------------------------------------------- void function_name() interrupt 1 { ... } --------------------------------------------------------------------

7) 82C55 82C55 is a device of 8-bit general input and output port of A, B, and C. It is often used for extension of GPIO (General Purpose I/O) such as 8051 ports. You can see the 8255 User's manual to know more detail.



As shown in the above circuit diagram, three 7-segment LED modules are connected with three ports of 82C55. To control them, set three ports to 'output' and write the value to each port. For this programming, you can see the operation table below. (See the macro of C_8255_A, C_8255_B, C_8255_C and C_8255_CR in Guru51.h)

A1 A0 /RD /WR Operation 0 0 0 1 Read from Port A 0 1 0 1 Read from Port B 1 0 0 1 Read from Port C 1 1 0 1 Read Control Register 0 0 1 0 Write to Port A 0 1 1 0 Write to Port B 1 0 1 0 Write to Port C 1 1 1 0 Write Control Register

8) 7-segment LED module

DP The structure of the 7-segment LED module is shown as follows. When A~G and DP become ‘HIGH’, the corresponding LED turns on. As shown in the circuit diagram of 82C55, ‘HIGH’ signal is required at the SEL_8255_IN_EX to drive the LED. By using above circuit diagram and the 7-segment LED module figure, you can know the rules of displaying numbers. For example, assume that you want to display ‘2’. To do this, A, B, D, E, and G should become “HIGH” and the rests should become ‘LOW’. Therefore port A should become ‘01011011(B)’.

9) LED control

As shown in the above figure, LED is connected with P1 ports of the 80C31. If you make

some of the bit in this port ‘LOW’, then current flows through LED and the corresponding LED turns on.



4. Pre-report 1) Pre-report (1) Investigate the meaning of following registers by referring to the 8051 User's Manual. - TCON, TMOD, TH1, TH0, TL1, TL0 - IE, IP (2) Investigate the operation characteristics of 8255 by referring to the 8255 datasheet. (3) To display the number 0~9 to the 7-segment LED module of the experiment board, what kind of binary values should be written to those address? (4) When you define the variables in KEIL uVisionII compiler, you can use the keywords such as xdata, pdata, and data. Investigate what they are and what the differences are. 2) Experimental devices and components - COMPACT51 board - KEIL uVisionII program - PC - UART cable to connect the COMPACT51 board with PC

5. Demonstration 1) Problem (A) 7-Segment Implement the stopwatch. The timer starts when INT0 button is pushed, and the timer stops when INT0 button is pushed again. The timer becomes “0.00” (cleared) when TIMER0 button is pushed. Time is represented by the three 7 segment LED modules. During the first 10 seconds, the leftmost module represents ‘second’, the middle one represents ‘1/10 second’, and the rightmost one represents ‘1/100 second’. At this time, there is a decimal point between leftmost one and right 2 logics, i.e., between 1 second and 1/10 second. After 10 seconds, 2 left modules represent the ‘second’ level and the rightmost one represents ‘1/10 second’. In other words, the position of a decimal point shifts right and the number of 1/100 second disappears. (Resolution is decreased, and scale is increased.) Then, the timer can represent up to 99.9 second.

(B) LED During stopwatch operates, 8 LED modules present the number of 7 segment LED as binary number. 4 LED modules present multiples of 10 second, and other 4 LED modules present multiples of 1 second. For example, if number of 7 segment is 37.2, 8 LED modules should be 0011 0111. Implement 0 as turned-off LED and 1 as turned-on LED. Don’t express multiples of 0.1 second and 0.01 second, and express only multiples of 1 second and 10 second. When reset button is pushed, 8 LED modules should be turned off.



2) Useful tip for experiments (1) Setup jumpers as follows.

INT1 SRC TO SRC

(2) Handle the button input

As shown in above figure, INT0 button is connected with INT0 (External interrupt of 80C31), so interrupt handler of interrupt 0 can treat this input. Current jumper setting makes TIMER0 button input connect with T0 of 80C31. This pin is multiplexed with P3.4 (4th port of 3rd pin), so you can read the value of P3.4 to check whether this button is pushed or not. (HINT: Set “sbit TIMER0_BUTTON = P3^4;” and read the value of TIMER0_BUTTON. If you get ‘0’, then the button is pushed.) (3) Pseudo-code (There is no need to follow this process. This is just hint!) -------------------------------------------------------------------- #include <reg51.h> #include "COMPT51.h" sbit TIMER0_BUTTON = P3^4; void button_int_handler() interrupt 0 { ... } void timer_int_handler() interrupt 1 { ... } void ResetTimer0(void) { /* Select mode, Use internal clock as a input clock of the timer */ /* Load the initial value of the timer */ /* Timer0 interrupt disable */ /* Stop timer0 */



} void main(void) { SRRW1 |= 0x02; /* 7 segment logic enable */ C_8255_CR = ...; /* 7 segment logic setup */ C_8255_A = ....; C_8255_B = ...; C_8255_C = ...; /* 7 segment logic initial value */ /* Set the external interrupt0 signal, enable */ while (1) { ... if (there is a need of change the value of 7 segment logic) { C_8255_A = ...; C_8255_B = ...; C_8255_C = ...; } if (if INT0 button is pushed) { ... } if (if TIMER0 button is pushed) { ... } } } -------------------------------------------------------------------- ※ According to the design, interrupt handler includes many tasks or main routine includes many tasks. This is a design choice, and you can select the right choice.

6. Consideration

1) How precise do you think the implemented stopwatch is? What are the factors that disturb the accuracy of the stopwatch? 2) How do you think the other interrupt is occurred when the interrupt handler is already busy?

7. Reference 1) 8051 User’s manual 2) 8255 User’s manual 3) 8051 & C Programming, Moon Wang-hwan, Sehwa

Experiment 3

Documents

h address

external interrupt

interrupt type

interrupt vectors

interrupt operation

uart interrupt vector

ee306 digital electronic

memory address