P89LPC935 Microcontroller Tutorial - gmitWEB

P89LPC935 Microcontroller Tutorial 

Agenda 

• Basic Architecture of the P89LPC935 microcontroller 

– Memory, Input/Output Ports, Clocking, Timers 

• Writing C code for 8051 based microcontrollers 

– C51 language extensions 

• Sample Diploma Project 

– The Keyless lock 

Diploma Project Tutorial 1

MCB900 Board 


MCB900 Features 

• RS232 driver provides a standard COM port interface. 

• 8 buffered LEDs display I/O port 2 status information. 

• Potentiometer and Jumper for ADC1 channel 2 analog input. 

• 3.3V low-drop regulator allows wide power supply range (5V-9VDC). 

• Jumpers for flexible ISP and debug configurations. 

• All P89LPC935/P89LPC932 pins available on flexible connection area. 

• Prototyping area: 55mm x 25mm (2.1" x 1.0"). 


P89LPC935 Microcontroller Basic Architecture 

• 8-bit microcontroller 

• 8 KByte Flash Program memory 

• 256 Byte Data Memory (RAM) + 512 bytes auxiliary RAM (XDATA) 

• 512 Byte EEPROM 

• 3V device but I/O pins are 5V tolerant 

• Up to 26 input/output pins (4 ports P0 to P3) 

• 2 16-bit timer/counters 

• UART for serial interfacing 

• 15 interrupt sources, 5 priority levels 

• 2 clock machine cycle 

– All instructions execute in 1, 2 or 4 machine cycles 

– Instructions execute 6 times faster than 8051 

• Program and data memory may not be expanded externally 


P89LPC935 Microcontroller Advanced Architecture 

• In-System Programmable (ISP) 

• In-Application Programmable (IAP) 

• Watchdog timer 

• Real Time Clock 

• On-chip power-on reset 

• I2C port 

• SPI port 

• Dual 4-input multiplexed 8-bit ADCs 

• Dual DAC 

• 2 Analog Comparators 


P89LPC935 Microcontroller Advanced Architecture 


Memory Organisation 

• The 8051 architecture supports 2 parallel memory spaces 

– Program memory used for code and constant storage 

– Data memory used for variable storage 


Memory Organisation 

• Data Memory 

– 256 bytes of on-chip data RAM 

• Used for stack, registers, bit addressable memory and variables 

• Upper 128 bytes is indirectly addressable only 

– SFRs (Special Function Registers) 

• Used for control and status 

– 512 bytes of on-chip auxiliary data RAM 

• Duplicates 8051 off-chip data memory 

• Slower access than directly accessible memory 

– 512 bytes data EEPROM 

• Non-volatile data memory 

• Accessed by SFR only 

• Program Memory 

– 8KByte flash memory 

– Used for application code and optionally for user data 

– ISP serial loader stored here 


Input/Output Ports 

• P89LPC935 is a 28 pin device 

• Up to 26 of the pins are available for input/Output 

– 3 8-bit ports P0, P1, P2 

• Port pins are labeled Px.0 to Px.7 where x is the port number 

• P1.5 is input only and is unavailable if using an external reset 

• P1.2 and P1.3 may be configured as open-drain or input only 

– 2-bit port P3 

• P3 is unavailable if using an external crystal 





• P89LPC935 is a 3V device but the pins are 5V tolerant 

– Can interface directly to 5V TTL devices 

– Connecting a pin directly to 5V will increase power consumption 

– Each input can sink up to 20mA but the limit for the IC is 100mA 

– Configuration of the port pins may be changed to suit the hardware 

interface by writing to the Port Mode SFR registers. 


Port Configurations 

• Input Only 

– This is the default configuration at reset 

• Quasi-bidirectional 

– Standard 80C51 outputs 

– Strong pull-down can sink 20mA when output = ‘0’ 

– Weak pull-up can source 20uA when output = ‘1’ 

– Can be used to interface to TTL devices 

• Push-Pull 

– Used when more source current is required 

• Can source 3.2mA when outputting a ‘1’ 

– Strong pull-down can sink 20mA when output = ‘0’ 

• Open Drain 

– Needs an external pull-up to output a logic ‘1’ 

– Best solution when interfacing to 5V circuits 


Input/Output Port Configuration 

• On reset all port pins default to input 

• To change a port configuration the Port Output Mode Registers 1 & 2 must be 

written to. 

• A port may contain a mix of input and output pins. 

– e.g. configure P0.0 to P0.2 as input, all other Port 0 pins as quasibidirectional 

– P0M1 = 00000111 (0x07) 

– P0M2 = 00000000 (0x00) 


Interfacing Inputs to 5V Logic 

• Although the supply voltage is lower, the I/O-pins are 5V-tolerant. 

– i.e., the I/O stages cannot actively drive the outputs higher than the 

supply voltage, but they may be pulled to 5V externally. 

• The LPC935 inputs can be driven directly from the outputs of 5V logic 

families. 

• For a 3.3V power supply, the worst case Schmitt trigger input switching 

levels are V IL 

= 0.726V and V IH 

= 2.31V. 


Interfacing Outputs to 5V Logic 

• LPC935 output can drive a TTL input. 

• The output high level voltage (VOH) is not high enough to drive a CMOS 

input. 

• When outputting a 0, the LPC935 port pin can sink up to 20mA – total limit 

for the chip is 100mA. Bigger loads require external interface circuitry. 


Hardware Interfacing 

3.3V 

5V 

3.3V 

3.3V 

VDD 

VDD 

micro P0.1 

P0.1 

micro 

VSS 

VSS 

Direct hardware interface 

20mA max sink current 

Configure as quasi-bidir or 

Push-pull 

Interfacing to 5V hardware 

Configure as open-drain 

5V supply drives load 


89LPC935 Clock 

• A machine cycle is the minimum amount of time in which any P89LP935 

operation can execute 

– A machine cycle is 2 clock periods in duration 

– All instructions will execute in 1, 2 or 4 machine cycles 

– The internal timers operate every machine cycle if enabled 

• 3 clock source options 

– External crystal up to 12MHz 

– Internal RC 7.373MHz oscillator 

• Used on MCB900 board 

• Allows 2 XTAL pins to be used for input/output 

– Internal watchdog oscillator (400KHz) 

Use 33pF capacitor 

for 12MHz crystal 


Clock Configuration 


Keil C51 Cross Compiler 

• ANSI C Compiler 

– Generates fast compact code for the 8051 and it’s derivatives 

• Advantages of C over Assembler 

– Do not need to know the microcontroller instruction set 

– Register allocation and addressing modes are handled by the compiler 

– Programming time is reduced 

– Code may be ported easily to other microcontrollers 

• C51 supports a number of C language extensions that have been added to 

support the 8051 microcontroller architecture e.g. 

– Data types 

– Memory types 

– Pointers 

– Interrupts 


C51 Data Types 

Data Type Bits Range 

bit 1 0,1 

unsigned char 8 0 to 255 

signed char 8 -128 to +127 

unsigned int 16 0 to 65535 

signed int 16 -32768 to +32767 

unsigned long 32 0 to 4294967296 

signed long 32 -2147483648 to + 2147483647 

sbit 1 0,1 


C51 Memory Types 

• Memory type extensions allow access to all 8051 memory types. 

– A variable may be assigned to a specific memory space 

• code 

– Program memory. 

– unsigned char code const1 = 0x55; //define a constant 

– char code string1[] = “hello”; //define a string 

• data 

– Lower 128 bytes of internal data memory 

– unsigned int data x; //16-bit variable x 

• idata 

– All 256 bytes if internal data memory 

• bdata 

– Bit addressable area of internal data memory 

• xdata 

– External data memory (512 bytes of on-chip auxiliary data RAM) 


Example Code (1) 

//program to add 2 8-bit variables 

void main() 

{ 

unsigned char data num1, num2, result; 

} 

num1 = 10; 

num2 = 25; 

result = num1 + num2; 

• This code will use 3 bytes of internal data memory (00 to 7FH) 

• What happens if the result exceeds 255? 



//program to add 2 8-bit variables 

//a flag should be set if the result exceeds 100 

void main() 

{ 

unsigned char data num1, num2; 

unsigned int data result; 

bit overflow; 

} 

num1 = 10; 

num2 = 25; 

result = num1 + num2; 

if (result >100) 

overflow = 1; 


Accessing Port Pins 

• The microcontroller port should be configured at the start of the program. 

//configure port 2 to be quasi bi-directional 

P2M1 = 0x00; 

P2M2 = 0x00; //all 8 pins are quasi bi-directional 

• Writing to an entire port 

P2 = 0x12; 

//Port 2 = 12H (00010010 binary) 

P2 &= 0xF0; //clear lower 4 bits of Port 2 

P2 |= 0x03; //set P2.0 and P2.1 

• Reading from a port 

unsigned char data status; 

status = P1; //read from Port 1 



//Program to read from 8 switches connected to Port 1. The status of the switches 

//is written to 8 LEDs connected to Port 2. 

#include //SFR address definitions 

void main() 

{ 

unsigned char data status; //variable to hold switch status 

P1M1 = 0xFF; 

P1M2 = 0; 

//port 1 is input 

P2M1 = 0; 

P2M2 = 0xFF; 

//port 2 is output 

} 

//continuous loop to read switches and display the status 

while(1) 

{ 

status = P1; 

P2 = status; 

} 


Accessing Individual Port Pins 

• Writing to a port pin 

//write a logic 1 to port 0 pin 1 

P0^1 = 1; 

• In a program using lots of individual port pins it is better coding practice to 

name the pins according to their function 

sbit power_led = P0^1; 

power_led = 1; 

• Reading from a port pin 

//Turn on LED if switch is active 

sbit switch_input = P2^0; 

if (switch_input) 

else 





//program to flash an LED connected to Port 2 pin 0 every second 

#include 

sbit LED = P2^0; 

void delay(); 

void main() 

{ 

P2M1 = 0; 

P2M2 = 0; 

while (1) 

{ 

LED = 0; //LED off 

delay(); 

LED = 1; //LED on 

delay(); 

} 

} 

//Delay function 

void delay() 

{ 

……. 

} 


Generating Delays (1) 

• Use a for loop 

– Does not use any timer resources 

– Uses CPU resources while running 

• i.e. no other task can be performed during delay loop 

– Can result in large amounts of machine code being generated 

– Results may be different for different compilers 

• The following code results in a half second delay for the P89LPC935 

operating off the 7.373MHz RC oscillator 

void delay() 

{ 

unsigned int i; 

for (i=0; i < 50000; i++); 

} 



• Use assembly code 

– Use DJNZ loops to produce very compact code 

– Does not use timer resources 

– Uses CPU resources while running 

• i.e. no other task can be performed during delay loop 

• Use timer 0 or timer 1 

– Very efficient mechanism of producing accurate delays 

– Timer mode, control and counter registers must be configured 

– Timer run bit is used to start/stop the timer 

– The timer flag can be polled to determine when required time delay has 

elapsed 



• When enabled the timer counts from an initial value to FFFFH and then 

overflows to 0000H. The count is incremented every 2 clocks. 

• Delay = 2 x (2 16 – initial value)/fosc 

• Max. delay for a 7.373MHz crystal is 2 17 /7373000 = 17.118msec. 

• Calculate the initial value for a delay of 10msec 

– initial value = [2 16 – (0.01 x 7373000)]/2 

– Initial value = 28671 = 6FFFH 

– Load TL0 with FFH 

– Load TH0 with 6FH 


Using Timer 0 to Generate a Delay 

//function to generate a delay of x times 10msec 

void delay(unsigned char x) 

{ 

unsigned char z; 

TR0 = 0; 

//stop timer 

TF0 = 0; 

//clear timer flag 

TMOD = 0x01; 

//mode 1 - 16 bit timer 

TAMOD = 0; 

for (z=0;z

Connecting the MCB900 to your project circuit 

• Your project circuit board will most likely be powered from 5V. 

• The MCB900 board uses an on-board 3.3V supply. This is generated by 

regulating an external voltage source. 

– You can power the MCB900 using the supplied 6V mains regulator or 

using a power supply connected to the VIN terminals (next to the serial 

port connector). 

• Your project board must share the same ground as the MCB900 board. 

– Connect a wire from the MCB900 VSS terminal to the ground rail of your 

project board. 

• You may regulate the VIN power rail of the MCB900 to generate a 5V power 

rail for your project board (use a 7805 regulator). 

MCB VIN 

VIN 

GND 

VOUT 

+ 

10uF 

100nF 

5V 

MCB VSS 


Example Project 

• Keyless Doorlock 

– The door is opened by a 4 digit password entered via a keypad 

– 2 LED’s show the status of the lock 

– A solenoid is used to open/close the door latch

P89LPC935 Microcontroller Tutorial - gmitWEB

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