PIC16 Microcontrollers, Unit 4, Ch 2.3-2.4; Memory, Stack, and SFRs

Summary

In this lecture, Clint Halstead introduces microprocessors, focusing on program memory, the stack, data memory, and special function registers using the book 'Designing Embedded Systems with PIC Microcontrollers' by Tim Wilmshurst. He explains flash memory, program counters, the stack's LIFO structure, and their roles in executing and storing code. Halstead also covers SRAM, special function registers, and their use in interfacing with peripherals. He concludes by discussing the configuration word, its significance in setting microcontroller features, and its protection mechanisms against code theft.

Takeaways

• 📚 The lecture is an introduction to microprocessors, specifically using 'Designing Embedded Systems with PIC Microcontrollers: Principles and Applications, Second Edition' by Tim.
• 💾 The program memory is composed of non-volatile flash memory, which retains the program code even when power is removed from the chip.
• 🔢 The program memory space ranges from 0 to 3FF, providing approximately 1000 memory locations for storing code.
• 👉 The program counter is essential as it points to the next instruction in the program memory and starts at address zero upon power-up or reset.
• 📚 Section 2.3 and 2.4 of the book are being discussed, which cover program memory, stack, data memory, and special function registers.
• 🔠 The stack is a part of SRAM and operates on a LIFO (Last In, First Out) basis, crucial for function calls and preserving the state of the program counter.
• 🔄 The stack facilitates the 'push' and 'pop' operations, which save and restore the program counter's state during function calls.
• 🔩 Data memory is stored in SRAM, which is volatile and loses its values when power is removed, typically used for values set during program execution.
• 🌐 Special function registers are used for interfacing with peripherals, controlling aspects such as timers, port directions, and EEPROM memory.
• 🛠 The configuration word, found in program memory, determines certain operating features of the microcontroller and can be set during the programming process.
• 🔒 Code protection bits within the configuration word can prevent unauthorized reading of the microcontroller's program memory, protecting intellectual property.
• ⚙️ Oscillator configuration is vital as it dictates how the microcontroller operates, with options for internal (RC) and external oscillators.

Q & A

What is the primary function of program memory in a microcontroller?

The primary function of program memory in a microcontroller is to store the code, including assembler language code and C code, which the microcontroller executes.

Why is program memory often implemented using flash memory?

Program memory is often implemented using flash memory because it is non-volatile, meaning it retains the stored values even when the power is removed from the chip.

What does the program counter in a microcontroller do?

The program counter in a microcontroller points to the next instruction to be executed. It is set to zero upon power-up or reset, indicating the starting point of the code execution.

What is the significance of the stack in a microcontroller?

The stack in a microcontroller is used to store the return addresses during function calls, allowing the program to resume execution at the correct location after the function completes. It operates on a LIFO (Last In, First Out) principle.

How does the stack assist during function calls in a program?

During function calls, the current value of the program counter is pushed onto the stack to remember the current location in the code. After the function executes, the program counter is popped with the stored address, resuming the code execution from where it left off.

What is the role of the special function registers in data memory?

Special function registers in data memory control various aspects of the microcontroller's operation, such as timers, the program counter, status, file select for indirect addressing, and port control.

Why is SRAM considered volatile memory?

SRAM is considered volatile memory because it loses its stored values when power is removed from the chip, unlike non-volatile memory which retains values after power loss.

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

The TRISC register controls the direction of Port C on a microcontroller, determining whether the port operates as an input or output.

How does the configuration word in a microcontroller affect its operation?

The configuration word in a microcontroller determines certain operating features, such as code protection, power-up configuration, watchdog timer settings, and oscillator selection. It is set during the programming process and cannot be changed during normal operation.

What is the purpose of code protection bits in the configuration word?

Code protection bits in the configuration word prevent unauthorized reading of the microcontroller's program memory, protecting the intellectual property of the software developed for the microcontroller.

Why is it important to check the watchdog timer and oscillator settings when troubleshooting a microcontroller?

It is important to check the watchdog timer and oscillator settings when troubleshooting a microcontroller because incorrect settings can prevent the microcontroller from operating correctly. The watchdog timer may need to be disabled, and the oscillator must be correctly configured for the microcontroller to function.