PIC16 Microcontrollers, Unit 3, Ch 2.1-2.2; Block Diagram & Status Register

Summary

Clint Halstead's lecture introduces the PIC mid-range family of microprocessors, focusing on the PIC16F877A. The lecture covers the architecture, memory types including SRAM, EEPROM, and program memory, as well as special function registers. It highlights the simplicity of the 16F84A as a learning platform due to its direct applicability to larger microprocessors. The differences between various models, including the 16F84A, 16LF80A, and 16F87, are discussed, emphasizing the increased capabilities of the latter. The lecture also touches on the importance of the status register in indicating the result of ALU operations.

Takeaways

• 😀 The lecture is an introduction to microprocessors, focusing on the PIC mid-range family and specifically the 16F84A model.
• 📚 The reference material for the lecture is 'Microprocessors and Microcontrollers: Applications and Programming' by Tim Worrell, specifically the second edition.
• 💡 The 16F84A is chosen for its simplicity, making it easier for students to learn the fundamentals applicable to more complex microprocessors.
• 🔢 The 16F84A has 18 pins, operates at up to 20 megahertz, and includes 1k of program memory, 68 bytes of RAM, and 64 bytes of EEPROM.
• 🔌 The microprocessor features include an 8-bit timer, a 5-bit parallel port, and in-circuit serial programming (ISP).
• 🚀 Learning starts with the 16F84A and progresses to more advanced models like the 16F87 and 88, which add more peripherals.
• 🔋 The 16F87 model increases program memory to 4k, RAM to 368 bytes, and EEPROM to 256 bytes, and adds additional features like two parallel ports and more peripherals.
• 🔧 The 16F84A-4 variant has a different clock range, only going up to 4 megahertz, and an extended supply voltage range.
• 🔄 The 16F84 has a 10-bit ADC with multiplex capabilities, allowing one ADC to switch between different channels.
• 🔗 The block diagram of the 16F84A shows enhancements over previous models, including a 13-bit address bus and an increased stack level.
• 🛠 The status register is crucial for indicating the result of ALU operations, with specific bits for zero, digital carry, and carry out.

Q & A

What is the main topic of Clint Halstead's lecture?

The main topic of Clint Halstead's lecture is an introduction to microprocessors, specifically focusing on the PIC mid-range family and the 16F877A microcontroller from the book 'Microprocessors and Microcontrollers: Applications and Programming' by Tim Worrell.

Why is the 16F84A microcontroller chosen for the class?

The 16F84A microcontroller is chosen for the class because it is one of the simplest chips, making it easier for students to learn the fundamentals of microprocessors. The knowledge gained from studying this microcontroller is directly applicable to larger microprocessors as it forms part of their core.

What are the three different memory areas mentioned in the lecture?

The three different memory areas mentioned in the lecture are SRAM (Static Random Access Memory), EEPROM (Electrically Erasable Programmable Read-Only Memory), and Program Memory (flash memory).

What does ISP stand for in the context of the 16F84A microcontroller?

ISP stands for In-Circuit Serial Programming, which is a feature of the 16F84A microcontroller that allows for programming the device through two pins using a USB module connected to a computer.

What are the differences between the 16F84A and the 16LF80A?

The main difference between the 16F84A and the 16LF80A is the extended supply voltage range in the 16LF80A. Everything else, such as the number of pins, program memory, and features, remains the same.

How does the 16F877A differ from the 16F84A in terms of program memory and peripherals?

The 16F877A has quadruple the program memory compared to the 16F84A, allowing for larger code. It also has significantly more RAM, increased EEPROM size, and additional peripherals such as two parallel ports, three counter timers, a capture compare PWM module, two serial communication modules, and two download comparators.

What is the purpose of the status register in a microcontroller?

The status register in a microcontroller is used to indicate the results of arithmetic or logic operations, such as whether there was an overflow (carry), whether the result is zero, and other condition code flags that help in understanding the outcome of operations performed by the ALU (Arithmetic Logic Unit).

What is the significance of the 'C' bit in the status register?

The 'C' bit in the status register signifies a carry out from the most significant bit of the result. It is set to 1 if an overflow occurs during an arithmetic operation, indicating that the result is too large for the W register to hold accurately.

What is the role of the W register in the microcontroller?

The W register, also known as the working register, serves as a scratchpad register where the results of ALU operations, such as addition, subtraction, and logical operations, are stored temporarily.

How does the block diagram of the 16F84A differ from the 12F508 part discussed in chapter 1?

The block diagram of the 16F84A has a 13-bit address bus compared to the 12-bit address bus of the 12F508. It also has an increased program memory of 1K, an additional level in the stack, and an EEPROM section for non-volatile data storage.

What is the difference between RAM and EEPROM in terms of data retention?

RAM is volatile memory, meaning data stored in it will be lost when power is disconnected. In contrast, EEPROM is non-volatile memory, retaining data even when the power is turned off.

Outlines

00:00

📘 Introduction to Microprocessors and PIC Mid-Range Family

Clint Halstead introduces the lecture on microprocessors, focusing on the PIC mid-range family, specifically the 16F877A. The lecture is based on Tim Worrell's book, 'Microprocessors and Microcontrollers: Applications and Programming', and covers chapters on the PIC mid-range family and the 16F84A. The 16F84A is chosen for its simplicity, making it an ideal starting point for learning, with its features applicable to more complex microprocessors. The chip has 18 pins, operates up to 20 MHz, and includes 1k of program memory, 68 bytes of RAM, and 64 bytes of EEPROM. The lecture will delve into the technical architecture, memory, status registers, and various other aspects of the microprocessor, but will only cover the first two sections of the book.

05:01

🔌 Enhanced Features of the PIC 16F Microprocessors

The second paragraph delves into the enhanced features of the PIC 16F microprocessors, including the 16F84A and its variants. The 16F84A has been expanded to include more peripherals and advanced technology, such as two parallel ports, three counter timers, capture compare PWM modules, two serial communication modules, and nano watt technology. It also includes a software-selectable oscillator block and in-circuit serial programming. The 16F84A-4 variant has a different clock range, while the 16F87 increases program memory and RAM, and adds more peripherals. The paragraph also discusses the pin connections and features of the 16F microprocessors, such as dedicated master clear and oscillator pins, and the addition of an interrupt pin.

10:01

💾 Memory and I/O Features of the PIC 16F Microprocessors

This paragraph discusses the memory and I/O features of the PIC 16F microprocessors, highlighting the distinction between program code stored in flash memory and data stored in RAM, which is volatile and lost when power is disconnected. The EEPROM is introduced as a non-volatile memory that retains data even when power is off. The paragraph also explains the 13-bit address bus and the increase in memory from 52K to 1K, as well as the addition of an eighth level stack. The I/O ports are described, with the LSB of port B shared with the interrupt feature, and the status register is introduced, which includes condition code flags to indicate overflow and other arithmetic results.

15:02

🛠 Status Register and Microprocessor Block Diagram

The final paragraph focuses on the status register and the block diagram of the microprocessor. The status register's role in indicating the result of arithmetic or logic operations is explained, with emphasis on the zero, carry, and other condition code flags. The block diagram is used to illustrate the flow of data and instructions within the microprocessor, including the instruction register, RAM registers, and decode register. The lecture concludes with a mention of continuing the discussion in the next video series, highlighting the importance of understanding the microprocessor's architecture for effective programming and application.

Keywords

💡Microprocessors

Microprocessors are the central processing units of computers and other digital devices, performing the basic arithmetic, logic, and control operations. In the video, the lecturer is introducing the concept of microprocessors, specifically focusing on the PIC mid-range family, which is central to the theme of understanding the architecture and application of these devices.

💡PIC16F877A

The PIC16F877A is a specific model of microcontroller from the PIC family, used in the lecture as a reference point for teaching the basics of microprocessors. It is highlighted as a simple yet fundamental model that forms the basis for understanding more complex microprocessors, making it a key concept in the script.

💡Memory

Memory in the context of the video refers to the various types of storage within a microcontroller, including program memory, SRAM, EEPROM, and data memory. It is a fundamental concept as it explains how data and program instructions are stored and accessed within the microcontroller, crucial for its operation.

💡Status Register

The status register is a key component in microcontrollers that holds information about the results of the most recent operation, such as whether the result was zero or if there was a carry from an arithmetic operation. In the script, it is used to illustrate how the microcontroller manages and records the state of its operations.

💡SRAM

SRAM, or Static Random Access Memory, is a type of volatile memory used in microcontrollers for temporary data storage. The script mentions it as part of the memory architecture of the microcontroller, emphasizing its role in storing data that is lost when power is removed.

💡EEPROM

EEPROM stands for Electrically Erasable Programmable Read-Only Memory, a type of non-volatile memory that retains data even when power is off. The video discusses EEPROM as a part of the microcontroller's memory where data can be stored permanently, contrasting it with SRAM.

💡Program Memory

Program memory is where the microcontroller stores its program code, which is non-volatile and retains the code even when power is off. The script distinguishes program memory from data memory, highlighting its importance in storing the instructions that the microcontroller executes.

💡Special Function Registers

Special function registers are dedicated registers within a microcontroller that control specific functions or features. The script mentions these as part of the microcontroller's architecture, indicating their role in managing various operations and configurations.

💡Oscillator

An oscillator in the context of microcontrollers refers to the component that provides the clock signal, which is essential for the timing of operations within the device. The script discusses the oscillator as part of the microcontroller's configuration, showing its importance in setting the operational frequency.

💡Power-On Reset

Power-On Reset (POR) is a mechanism that resets the microcontroller to its initial state when power is applied. The script briefly mentions this concept, indicating it as part of the microcontroller's startup sequence and its role in ensuring the device begins operations correctly.

💡Interrupt

An interrupt is a signal that temporarily halts the normal flow of instructions within a microcontroller to allow a high-priority task to be executed. The script mentions the interrupt pin, indicating the microcontroller's capability to handle external events that require immediate attention.

Highlights

Introduction to microprocessors with a focus on the PIC mid-range family.

Discussion of the PIC16F877A microcontroller and its application in learning due to its simplicity and foundational role in understanding more complex microprocessors.

Explanation of the 16F84A microcontroller's features, including its 18 pins, 20 MHz operation, and memory configurations.

The direct applicability of knowledge gained from studying the 16F84A to more advanced microprocessors with additional peripherals.

Introduction to the different memory areas of the 16F84A: program memory, SRAM, EEPROM, and their respective sizes.

Description of the 16F84A's peripherals, such as an 8-bit timer, parallel ports, and in-circuit serial programming (ICSP).

Comparison between the 16F84A and its variants, such as the LF and A-4 versions, highlighting differences in voltage range and clock speed.

Detailed comparison of the 16F87 with the 16F84A, emphasizing the increased program memory, RAM, EEPROM, and additional peripherals.

Introduction of advanced features in the 16F87, such as counter timers, capture compare PWM module, and serial communication modules.

Explanation of the nano watt technology and software selectable oscillator block in the 16F87 for improved power efficiency and flexibility.

Overview of the 16F848's additional features, including 10-bit ADC channels and their multiplexing capabilities.

Discussion on the importance of the master clear and dedicated oscillator pins for improved functionality and ease of use.

Introduction to the block diagram of the 16F84A, outlining its core components and their interconnections.

Explanation of the 13-bit address bus and its enhancement over previous models with a 12-bit address bus.

Description of the EEPROM section, its purpose, and how it differs from volatile RAM in terms of data retention.

Importance of the status register in indicating the result of ALU operations and its role in managing condition code flags.

Overview of the lecture's continuation in a subsequent video series, indicating ongoing education on the topic.

Transcripts

hello this is Clint Halstead and I am

giving a lecture on introduction to

micro processors and I will be using

will be discussing pic16f877a plication

second edition by Tim Worrell sureste

this chapter is chapter two introducing

the pic mid-range family and the sixteen

f-84 a this chapter aims to introduce

the pig mid-range family to talk about

the overall tech architecture of the 16

f-84 a the memory things like status

register SRAM

EEPROM doli prom program memory stacked

special function registers addressing

configuration word oscillator pipelining

power on reset reset master clear

powerup timing

this lecture will only cover the first

two sections of the book so let's let's

get started ok so it's after 29 in the

book it shows a table of several

different parts this list shown here is

not exhaustive is not the exact one of

the book it only shows the first few but

the first part we'll talk about is the

16 f-84 a now this is the chip we're

going to start using in the class

it's the reason we're using is because

it's one

the simplest chips and by using this

simple chip it's going to make it easier

to learn but everything you learn about

this small smaller microprocessor is

directly applicable to the larger

microprocessors and it forms actually a

part of it so the larger processors have

more peripherals but the everything else

is the same that the the core of the

processor is the same the fundamentals

of how the stack work how the random

work all that stuff is the same the

commands the coding is exactly the same

so we can learn off of the simpler part

so it's not too overwhelming you and

then once we once we get finished

learning about how the this simpler chip

works then we will go up to the more

difficult parts more advanced parts like

the 16 F 87 and 88 which simply just

adds other peripherals so if we look

here the 16 f84 a has 18 pins operates

up to 20 megahertz as 1k of program

memory 68 bytes of RAM and 64 bytes of

double EEPROM so these represent the

three different memory areas it also has

a one 8-bit timer a five-minute parallel

port and an 8-bit parallel port it also

has in circuit serial programming that's

what the ISP stands for in circuit

serial programming okay now when we go

up to the LF part 16 and LF 80 for a

everything is the same except the

voltage has extended supply voltage

range okay and

then when we move on to the sixteen f-84

a - four it's the same but it has a

different clock range so the a - oh four

only goes up to four megahertz with this

when we go to the 16 F 87 then

everything else is this depends are the

same the clock speed is the same as the

84 but we we quadruple the program

memory so now you're able to code a

larger assembly language code or C code

whatever you're using also the number

the file registers also called ram has

been increased significantly to 368

bytes

also the doubling prompt size has

quadrupled to 256 bytes okay

also we've added quite a few more

peripherals and advanced technology so

notice that we have now two parallel

ports we have whereas before we had one

full parallel port and then a partial on

the other parallel port usually you know

eight bits is considered a full parallel

port so we have two full or we still

have actually we still have two parallel

ports as before but now we have three

counter timers instead of one we have to

capture compare PWM module switch before

we had none we have two serial

communication modules which before again

we had none to download comparators

which in the 84 again had none it also

has the nano nano watt technology which

is an improvement over the 84 we have a

software selectable oscillator block so

we can select our oscillator in software

programming by using this code or some a

similar language code to select the

oscillator block so that's a big

advantage and again we still have the

insert

get serial programming this just allows

you to program the part through two pins

clocking data using your your USB module

that connects to your computer so it's a

picot 2 or picot 3 or whatever whatever

you're using

then notice when you go to the 16 f-84

part you don't have 18 pins you still

have the 20 megahertz memories the same

but you add these 10-bit ADC channels so

you have 7 10-bit ADC channels so those

7 channels are MUX so it's not actually

seven individual it's not seven

enlarging dodol converters inside the

chip it's actually one analog to digital

converter but it's it's multiplex so

that you can switch channels between

pins so now the book talks about several

other different packages it talks about

the a 73 I'm sorry the 1680 73 16 f8 76

16 M 874 1608 77 and even the 16 f8 8x

parts and you can look at the book on

pages 29 30 for those also here this

slide is showing the pink connection

diagram notice that the first chip we

looked at was a a 12 F part which was in

chapter 1 so if you go back to chapter 1

you can pair that's on page 18 you'll be

able to see that the 12 F 508 part only

had 8 pins

and many of those pins were had

multifunction pen so that so for example

the 12 F 508 on page 18 had a Matt had a

master clear but it was shared with VPP

and on purpose GP 3 so notice on this

this part we have a dedicated master

clear right here on pan 1 2 3 4 pin 4 of

the master clear so that's that's a nice

feature also we have noticed that we

have a dedicated oscillator pins and

clock pans whereas before these pins

were shared with some other like output

pins input output pins so that's a

that's a really nice feature to have so

you're going to have to use up your

parallel port pins for your clock or

oscillator also notice on this chip that

you have also we've added an interrupt

pin this int which we'll talk about

interrupts later but on the RB 0 through

7 is called port B so this makes that

port B pin 7 8 9 10 11 12 13 it's

considered port B and then we have a

port a which is 17 18 1 2 and pin 1 2

and 3 that gives us port a so it's a 5

bit of course we have supply voltage VDD

and then we have ground VSS and that

makes up pretty much all the pins ok

all right so and this chip is the 16

f-84 8 by the way which is going to be

the first chip that we talked about and

we've got to get some examples in coding

in the class so now if we look at the

block diagram for this 16 f-84 a we can

see that it has basically the same

features as the the 12 F part that we

saw in chapter 1 but we've seen a few

and a few enhancements will talk about

those just a little bit first off we

went to a 13 bit address bus whereas

before we had a 12 so that's one of the

first things we noticed here

also if you look on page 20 and compared

to the 12 F 508 part well we only had

five 12km memory but here we have one K

of memory so that that has been

increased as well also we've added an

eighth level stack whereas before we

only had two okay also we have added an

EEPROM section this is a electronic

electronically erasable programmable

read-only memory that's what W problem

stands for and it's connected here to

the data bus so you can you can send a

data word here from the data bus and you

can send the data address and you can

access your EEPROM this is data you can

store to the chip that will will not go

away when power is removed from the chip

now any day that you have in the RAM

will go away when the power is

disconnected okay so many times here in

the EEPROM we may want to store messages

like hello this is rocket sassy program

rocket or

something like that or maybe your name

or the name of your project whereas your

your seat code or your assembly language

code is going to go in your flash memory

here now this is non-volatile as well

which means this memory will be retained

when you turn the power off so the flash

memory and the EEPROM memory will be

remembered when power goes away when you

flip the off switch on or when you put

the off switch the only thing that's

going to go away is your RAM okay so

this is the memory that goes away when

you turn off power this stores your your

C code or your assembly language code

this stores data so we make a

distinction between program code and

data okay another thing too I want to

highlight here is you have your four

bits of i/o ports so this is called your

port a our a 3 to our a 0 as for bits

and then we have our B 0 to our b7

that's port B notice that the int and

external interrupts can be is

multifunction with our B 0 so the LSB of

our port the port B is shared with

interrupt feature if you want so this

would be selected in your software you

have to select what feature you want

inside of your software code which would

be configured up here so I get last week

we talked about master clear and your

power up power on reset your oscillator

and all that stuff so I'm not going to

talk

that again I do want to highlight just

one more time your W register your W

register is your scratch pad registers

sometimes called and it's the result of

your ALU so your ALU is your arithmetic

logic unit which is the result of any

addition subtraction and or whatever

logic functions is gonna be in the

Debbie register if you can imagine you

the results your neww register you can't

really there's more information that you

may need other than just a result for

example if you month if you add to two

numbers here Nate bit number another

8-bit number it is possible that that

number could overflow and that the

values could in the W register could be

incorrect if you go back to binary

addition it's possible if you add you

know it for example a number of you know

250 plus 100 while you would go above

256 so you're you only have 8 bits on

your W register so your result in the W

register may be incorrect so we need to

have a way of indicating whether or not

you overflow your W register so the way

we do that is with what's called a

status register and you can see that

right here so we want to talk a little

bit about the status register today

so your status register looks like this

it has eight bits and we want to talk

about the first three bits that has

tells you whether result in the in your

W register is zero or not so if your

result is zero that's going to be

indicated by this bit zero one two so

this bit Fitzie it's called bit too

it says the result of and if arithmetic

or logic operation is zero so if that is

set to one then you have the W register

is 0 otherwise it would be if this bit

is set to 0 that means well the result

is not zero and four bit 1 which is a

bit one this is called a digital era and

this means that a carry from the fourth

low order bit of the result occurred so

I carry out from the 4th low order bit

of there's over code let's talk about

the 4th loader bid is the 4th loader low

order bit of the W register ok and then

ik and then bit 0 which is the C bit

here is the carry bar a bit it means

that they carry out from the most

significant bit of result occurred

occurred so that would be like if you

added two numbers that were too large

for the W register and if you added

those numbers then you would have a bit

shift out of the the most significant

bit position and the result of being

correct so you need to know that so this

C bit should be a 1 if that occurs ok so

these are called your condition code

flags that's called the status register

again the status register is located

here in the block diagram ok

also I'm just wanting to be tell a

little bit more about the block diagram

notice that the in the flash memory the

instruction word here flows out here

this is where the address comes into the

flash memory this is where the data

comes out so this is a 14 bit

and it comes into this instruction

register and then from instruction

register like we talked about last week

you have you have a literal data that

flows along this line you have address

information that flows along this line

gets mixed into your RAM registers and

then you have instruction information

that flows into the decode register ok

so that is it for sections 1 and 2 of

the room source textbook and this

lecture will be continued in a next

video series thank you