Microcontrollers Lecture L12.2 Section 12.2

Microcontrollers Microcontrollers vs. Microprocessors Two standard architectures PIC microcontroller 68HC12 Microcontroller BASIC Stamp Jstamp What’s the Difference

Microcontrollers Microprocessor – Performs computing function for different architectures of memory, input/output ports, devices, and communication ports Microcontroller –Performs computing functions and contains onchip memory, input/output ports, devices, and communication ports. –Resources are limited

Microcontrollers

Desktop Computers –Different architectures/configurations of memory, devices, and ports –Microprocessor is a general purpose computing machine Embedded Systems –Includes coffee makers, burglar alarms, TV remote controls, simple robots, etc… –Easier to use a microcontroller with limited functionality and onchip resources No need to select/design a board with memory, etc… Ready to program

The PIC Microcontroller Very common microcontroller Made by Microchip Technology Over 180 different microcontrollers Available in different configurations of on-chip resources Timers, Drivers for writing to Liquid Crystal Displays, USB and TCP/IP interfaces, temperature sensors, and more Packaged in 8- to 84-pin configurations Contains from 1 KB to 128 KB memory Available in 8 and 16 bits

Microcontrollers PIC controllers have a Harvard Architecture Architecture used for Desktop personal computers

Microcontrollers What do you think are some advantages/disadvantages of these architectures?

PIC

368 Bytes of Memory for Data 8 KB of Memory For Programs 14-bit program words

PIC Similar to Lab 10

PIC The Instruction Set

3 Types of instructions

Byte-oriented instructions fff ffff – the 7-bit address for which location in the register file (memory) contains the data of interest d – if d = 0, then the answer will be stored in the W register, otherwise if d = 1, then the answer will be stored in the memory location selected by fff ffff.

Byte-oriented instructions If ADDWF is encoded as machine code: d = 0 memory location = 0A d Memory address

Byte-oriented instructions If ADDWF is encoded as machine code: d = 0 memory location = 0A W reg is added to RF[0A] and the answer is placed in W reg OPCODE = 070A

Byte-oriented instructions If ADDWF is encoded as machine code: d = 1 memory location = 0A W reg is added to RF[0A] and the answer is placed in RF[0A] OPCODE = 078A

Byte-oriented instructions For ADDWF, we have seen type machine codes: 070A – add RF[0A] to W reg and place answer in W reg 078A – add RF[0A] to W reg and place answer in RF[0A] … and there are many more where that came from…

Bit-oriented instructions bbb – selects the bit that will be operated on ffffff – selects the memory location of the data to be operated on For example, BCF encoded as the machine code: Bit # Memory address

Bit-oriented instructions bbb – selects the bit that will be operated on ffffff – selects the memory location of the data to be operated on For example, BCF encoded as the machine code: Bit 7 (MSB) of the Byte in RF[0B] is cleared to zero OPCODE = 138B

Literal and Control instructions X – means don’t care K’s – the literal Literal means ‘inline data’ like in the 8086 when we used MOV AX, 0FFFF to move FFFF into AX, FFFF was the Literal or inline data.

Literal and Control instructions X – means don’t care K’s – the literal For example, if ADDLW is encoded as machine code: Inline Data

Literal and Control instructions X – means don’t care K’s – the literal For example, if ADDLW is encoded as machine code: F is added to the value in W reg and the sum is put in W reg OPCODE = 3E0F

Development Tools for PIC There is a Windows Development Environment for the PIC Controller

BASIC Stamp Based on 8-bit PIC 14-pin microcontroller Can be programmed using the BASIC language –It has a BASIC language interpreter built-in

BASIC Stamp

Online Interpreter Most microcontrollers do not have a built-in interpreter of any kind Usually source code written in higher level languages are compiled to a microcontrollers machine code BASIC Stamp is inexpensive and easy to program for small applications

JStamp Directly executes Java bytecodes

JStamp

The Java Processing Core

What’s the Difference When selecting a microcontroller there are several factors that need to be considered There are many microcontrollers available Each brings advantages and disadvantages

Considerations Cost –Prototype –Mass Production Inputs –Correct # of inputs –Digital / Analog

Considerations Outputs –Correct # of Outputs –Digital / Analog Processing Speed and Function –Adequate Computational Power –Upgrading a processor due to choosing the incorrect processor can be costly Rework of written programs

Considerations Memory –Programs –Data –Enough internal memory and/or can address enough external memory Ports –Correct ports for communicating with other devices Parallel Serial

Considerations Support –Online Forums Free source code Frequently Asked Questions (FAQs) –Support from Vendor –Pre-developed software Availability –Volumes – lead time

Considerations Extensibility –Future growth –Avoid changing microcontrollers in future releases Development Tools –Language (C / BASIC / Java) –Development Environment Debugging

Considerations Other technical requirements –Power Consumption Portable applications –Operating Voltage Compatible with other circuits