An introduction to the PIC microcontroller

EE2801 -- Lecture 19

An Introduction To The

PIC Microcontroller

EE2801-L19P01

The PIC 16F87X Series Microcontroller

The PIC Series of microcontrollers is representative of the current industry trend towards highly capable, low-cost, processors for embedded applications. Although they are not suited to everything, they can do a lot!

However, they are quite a bit different that what we’re used to at this point!

Some of the characteristics of the PIC 16F87X series are:

Only 35 instructions!

All instructions (except branch) execute in 1 cycle. Eight level deep hardware stack.

4K word program space, 192 bytes of RAM

Internal A/D converter, serial port, digital IO ports, timers, and more!

Remember, what you are about to see will look completely different than anything you’ve seen so far!

However, all of the techniques we’ve used and the concepts we’ve learned are directly applicable!

EE2801-L19P02

The PIC 16F87X Family Capabilities

The following table summarizes the capabilities of the PIC16F87X series components. Although when we use the compiler we’ll set the processor type to 16F877, that’s only because each component in the family is compatible. The actual version we’ll use is the PIC16F874:

PIC16F87X

Key Features
PICmi croô Mid-Range Referenc e	PIC16F873	PIC16F874	PIC16F876		PIC16F877
Manual (DS33023)
Operating Frequency	DC - 20 MHz	DC - 20 MHz	DC - 20 MHz		DC - 20 MHz
Resets (and Delays)	POR, BOR	POR, BOR	POR, BOR		POR, BOR
	(PWRT, OST)	(PWRT, OST)	(PWRT, OST)		(PWRT, OST)
FLASH Program Memory	4K	4K	8K		8K
(14-bit words)
Data Memory (bytes)	192	192	368		368
EEPROM Data Memory	128	128	256		256
Interrupts	13	14	13		14
I/O Ports	Ports A,B,C	Ports A,B,C,D,E	Ports A,B,C		Ports A,B,C,D,E
Timers	3	3	3		3
Capture/Compare/PWM modules	2	2	2		2
Serial Communications	MSSP, USART	MSSP, USART	MSSP, USART		MSSP, USART
Parallel Communications	-	PSP	-		PSP
10-bit Analog-to-Digital Module	5 input channels	8 input channels	5 input channels	8	input channels
Instruction Set	35 Instructions	35 Instructions	35 Instructions		35 Instructions

EE2801-L19P03

The PIC16F874 Architecture

13		Data Bus	8
	Program Counter
FLASH
Program
Memory		RAM
	8 Level Stack
		File
	(13-bit)
		Registers

Program

14

RAM Addr (1)

9

Bus

Addr MUX

Instruction reg

Direct Addr 7

8

Indirect

Addr

FSR reg

8

STATUS reg

		Power-up	3	MUX
		Timer
	Instruction	Oscillator
	Decode &	Start-up Timer		ALU
	Control
		Power-on
			8
		Reset
	Timing	Watchdog		W reg
	Generation	Timer
OSC1/CLKIN		Brown-out
OSC2/CLKOUT		Reset
		In-Circuit
		Debugger
		Low-Voltage
		Programming		Parallel Slave Port
		MCLR VDD, VSS
Timer0	Timer1	Timer2		10-bit A/D

Data EEPROM		CCP1,2		Synchronous		USART
				Serial Port

PORTA
	RA0/AN0
	RA1/AN1
	RA2/AN2/VREF-
	RA3/AN3/VREF+
	RA4/T0CKI
	RA5/AN4/SS
PORTB	RB0/INT
	RB1
	RB2
	RB3/PGM
	RB4
	RB5
	RB6/PGC
PORTC	RB7/PGD
	RC0/T1OSO/T1CKI
	RC1/T1OSI/CCP2
	RC2/CCP1
	RC3/SCK/SCL
	RC4/SDI/SDA
	RC5/SDO
	RC6/TX/CK
	RC7/RX/DT
PORTD

RD7/PSP7:RD0/PSP0

PORTE

RE0/AN5/RD

RE1/AN6/WR

RE2/AN7/CS

Devi ce	Program	Data Memo ry	Data
	FLASH		EEPROM
PIC16F874	4K	192 Bytes	128 Bytes
PIC16F877	8K	368 Bytes	256 Bytes

EE2801-L19P04

The PIC16F874 Program And Stack Memory Map

Instead of having a large memory space outside the processor and a small memory space inside the processor (the registers) like we do in the 80x86, the PIC does two things. First, it divides memory into two main spaces: program memory and data memory. For program memory, the map looks as follows:

PC<12:0>

CALL, RETURN

13

RETFIE, RETLW

Stack Level 1

Stack Level 2

		Stack Level 8
		Reset Vector	0000h
		Interrupt Vector	0004h
			0005h
On-Chip		Page 0

07FFh

Program

Memory	0800h
	Page 1
	0FFFh
	1000h

Note: The unused space in this memory map is used in other family processors.

1FFFh

EE2801-L19P05

The PIC16F874 Register File Map

	Indirect addr.(*)	00h
	TMR0	01h
		02h
	PCL
		03h
	STATUS
		04h
	FSR
		05h
	PORTA
		06h
	PORTB
		07h
	PORTC
		08h
	PORTD (1)
	PORTE (1)	09h
	PCLATH	0Ah
		0Bh
	INTCON
		0Ch
	PIR1
		0Dh
	PIR2
		0Eh
	TMR1L
		0Fh
	TMR1H
		10h
	T1CON
		11h
	TMR2
		12h
	T2CON
		13h
	SSPBUF
		14h
	SSPCON
		15h
	CCPR1L
		16h
	CCPR1H
		17h
	CCP1CON
		18h
	RCSTA
		19h
	TXREG
		1Ah
	RCREG
		1Bh
	CCPR2L
		1Ch
	CCPR2H
		1Dh
	CCP2CON
		1Eh
	ADRESH
		1Fh
	ADCON0
		20h
	General
	Purpose
	Register
	96 Bytes
		7Fh
	Bank 0

Indirect addr.(*)	80h
OPTION_REG	81h
PCL	82h
STATUS	83h
FSR	84h
TRISA	85h
TRISB	86h
TRISC	87h
TRISD (1)	88h
TRISE (1)	89h
PCLATH	8Ah
INTCON	8Bh
PIE1	8Ch
PIE2	8Dh
PCON	8Eh
	8Fh
	90h
SSPCON2	91h
PR2	92h
SSPADD	93h
SSPSTAT	94h
	95h
	96h
	97h
TXSTA	98h
	99h
SPBRG
	9Ah
	9Bh
	9Ch
	9Dh
ADRESL	9Eh
	9Fh
ADCON1
	A0h
General
Purpose
Register
96 Bytes
	FFh
Bank 1

Indirect addr.(*)	100h
	101h
TMR0
	102h
PCL
	103h
STATUS
	104h
FSR
	105h
	106h
PORTB
	107h
	108h
	109h
	10Ah
PCLATH
	10Bh
INTCON
	10Ch
EEDATA
EEADR	10Dh
	10Eh
EEDATH
	10Fh
EEADRH
	110h

120h

accesses 20h-7Fh

16Fh

170h

17Fh

Bank 2

	File
Address
Indirect addr.(*)	180h
OPTION_REG	181h
PCL	182h
STATUS	183h
FSR	184h
	185h
TRISB	186h
	187h
	188h
	189h
PCLATH	18Ah
INTCON	18Bh
EECON1	18Ch
EECON2	18Dh
Reserved(2)	18Eh
Reserved(2)	18Fh
	190h

1A0h

accesses A0h - FFh

1EFh

1F0h

1FFh

Bank 3

EE2801-L19P06

“Registers” In The PIC Microcontrollers

Value on:

Value on

Addr es

all other

Name

Bi t 7

Bit 6

Bit 5

Bit 4

Bit 3

Bit 2

Bit 1

Bit 0

POR,

s

resets

BOR

(2)

Bank 0

00h(4)

INDF

Addressing this location uses contents of FSR to address data memory (not a physical register)

0000

0000

0000

0000

01h

TMR0

Timer0 moduleís register

xxxx xxxx

uuuu uuuu

02h(4)

PCL

Program Counter's (PC) Least Significant Byte

0000

0000

0000

0000

03h(4)

STATUS

IRP

RP1

RP0

TO

PD

Z

D

C

C

0001

1xxx

000q

quuu

04h(4)

FSR

Indirect data memory address pointer

xxxx xxxx

uuuu uuuu

05h

PORTA

ó

ó

PORTA Data Latch when written: PORTA pins when read

--0x 0000

--0u 0000

06h

PORTB

PORTB Data Latch when written: PORTB pins when read

xxxx xxxx

uuuu uuuu

07h

PORTC

PORTC Data Latch when written: PORTC pins when read

xxxx xxxx

uuuu uuuu

08h(5)

PORTD

PORTD Data Latch when written: PORTD pins when read

xxxx xxxx

uuuu uuuu

09h(5)

PORTE

ó

ó

ó

ó

ó R

E2

RE1

RE0

---- -xxx

---- -uuu

0Ah(1,4)

PCLATH

ó

ó

ó

Write Buffer for the upper 5 bits of the Program Counter

---0 0000

---0 0000

0Bh(4)

INTCON

GIE

PEIE

T0IE

INTE

RBIE

T0IF

INTF

RBIF

0000

000x

0000

000u

0Ch

PIR1

PSPIF(3)

ADIF

RCIF

TXIF

SSPIF

CCP1IF

TMR2IF

TMR1IF

0000

0000

0000

0000

0Dh

PIR2

ó

(6)

ó

EEIF

BCLIF

ó

ó

CCP2IF

-r-0 0--0

-r-0 0--0

0Eh

TMR1L

Holding register for the Least Significant Byte of the 16-bit TMR1 register

xxxx xxxx

uuuu uuuu

0Fh

TMR1H

Holding register for the Most Significant Byte of the 16-bit TMR1 register

xxxx xxxx

uuuu uuuu

10h

T1CON

ó

ó

T1CKPS1

T1CKPS0

T1OSCEN

T1SYNC

TMR1CS

TMR1ON

--00 0000

--uu uuuu

11h

TMR2

Timer2 moduleís register

0000

0000

0000

0000

12h

T2CON

ó

TOUTPS3

TOUTPS2

TOUTPS1

TOUTPS0

TMR2ON

T2CKPS1

T2CKPS0

-000 0000

-000 0000

13h

SSPBUF

Synchronous Serial Port Receive Buffer/Transmit Register

xxxx xxxx

uuuu uuuu

14h

SSPCON

WCOL

SSPOV

SSPEN

CKP

SSPM3

SSPM2

SSPM1

SSPM0

0000

0000

0000

0000

15h

CCPR1L

Cap ture/Compare/PWM Register1 (LSB)

xxxx xxxx

uuuu uuuu

16h

CCPR1H

Cap ture/Compare/PWM Register1 (MSB)

xxxx xxxx

uuuu uuuu

17h

CCP1CON

ó

ó

CCP1X

CCP1Y

CCP1M3

CCP1M2

CCP1M1

CCP1M0

--00 0000

--00 0000

18h

RCSTA

SPEN

RX9

SREN

CREN

ADDEN

FERR

OERR

RX9D

0000

000x

0000

000x

19h

TXREG

USART Transmit Data Register

0000

0000

0000

0000

1Ah

RCREG

USART Receive Data Register

0000

0000

0000

0000

1Bh

CCPR2L

Cap ture/Compare/PWM Register2 (LSB)

xxxx xxxx

uuuu uuuu

1Ch

CCPR2H

Cap ture/Compare/PWM Register2 (MSB)

xxxx xxxx

uuuu uuuu

1Dh

CCP2CON

ó

ó

CCP2X

CCP2Y

CCP2M3

CCP2M2

CCP2M1

CCP2M0

--00 0000

--00 0000

1Eh

ADRESH

A/D Result Register High Byte

xxxx xxxx

uuuu uuuu

1Fh

ADCON0

ADCS1

ADCS0

CHS2

CHS1

CHS0

GO/

ó A

DON

0000

00-0

0000

00-0

DONE

EE2801-L19P07

How To Deal With All These Registers!!!

R/W-0

R/W-0 R/W-0

R-1

R-1

R/W-x

R/W-x

R/W-x

IRP

RP1

RP0

TO

PD

Z

DC

C

R = Readable bit

W = Writable bit

bit7

bit0

U = Unimplemented bit,

read as ë0í

- n= Value at POR reset

bit 7:

IRP:

Register Bank Select bit (used for indirect addressing)

1 = Bank 2, 3 (100h - 1FFh)

0 = Bank 0, 1 (00h - FFh)

bit	6-5:	RP1:RP0: Register Bank Select bits (used for direct addressing)
		11 = Bank 3 (180h - 1FFh)
		10 = Bank 2 (100h - 17Fh)
		01 = Bank 1 (80h - FFh)
		00 = Bank 0 (00h - 7Fh)
		Each bank is 128 bytes
bit	4:	TO: Time-out bit
		1	= After power-up, CLRWDT instruction, or SLEEP instruction
		0	= A WDT time-out occurred
bit	3:	PD: Power-down bit
		1	= After power-up or by the CLRWDT instruction
		0	= By execution of the SLEEP instruction
bit	2:	Z: Zero bit
		1	= The result of an arithmetic or logic operation is zero
		0	= The result of an arithmetic or logic operation is not zero
bit	1:	DC: Digit carry/borrow bit (ADDWF, ADDLW,SUBLW,SUBWF instructions)
		(for borrow the polarity is reversed)
		1	= A carry-out from the 4th low order bit of the result occurred
		0	= No carry-out from the 4th low order bit of the result
bit	0:	C: Carry/borrow bit (ADDWF, ADDLW,SUBLW,SUBWF instructions)
		1	= A carry-out from the most significant bit of the result occurred
		0	= No carry-out from the most significant bit of the result occurred

Note: For borrow the polarity is reversed. A subtraction is executed by adding the twoís complement of the second operand. For rotate ( RRF, RLF) instructions, this bit is loaded with either the high or low order bit of the source register.

EE2801-L19P08

An Example PIC-Based System

EE2801-L19P09