Diary of a Trainee Electronics Engineer: April 2017Follow article
Easter trips and PIC & PLC comparisons
Is it just me or is this year flying by? I can’t believe were already in May, and now that Easter is over there isn’t another major holiday until Halloween!
It’s daunting to think that I’ve almost completed my HND, as little as six months ago did this point feel like a very long way off in the future. With just one more assignment to hand in before I finish, I can then prepare to head off to university in September to top-up to the BEng.
Over the past year of the HND course we have spent a lot of time learning about PLCs, including their application, architecture, advantages and disadvantages. In the final assignment for the PLCs unit we were given the task to compare PICs — a type of microprocessor we learned about last year — with PLCs.
While the work I’ve submitted so far this year has been pretty varied, I really enjoyed bringing things which I have learned in several modules over the past two years together in this final assignment. For the purposes of which I was asked to evaluate peripheral interface controllers and other programmable devices as programmable devices and embedded controllers, as well as compare the operation, functionality, advantages and limitations of PLC simulators. Here we will just look at PICs and how they compare to PLCs.
What is a PIC?
A Peripheral Interface Controller, most commonly known as a PIC, is a type of microcontroller which is used in many electronic applications. Microcontrollers are found in many applications in modern times, any device which has the capability to display, measure, calculate or store information may well contain a microcontroller within its circuitry.
Image source: http://microcontrollerslab.com
I like to think of a microcontroller as a minimal single chip version of a modern PLC, this contains the processor and all other supporting components in order to enable this to interface with external peripherals.
Peripheral Interface Controllers (PICs), sometimes referred to as programmable intelligent computers, are one of the advanced microcontrollers developed by Microchip Technologies. These microcontrollers are widely used in modern electronics applications, integrating all type of advanced interfacing ports and memory modules. The PIC is known for being more advanced than traditional microcontrollers such as the INTEL 8051. Similarly, to normal microcontrollers the PIC also combines a microprocessor unit called CPU and is integrated with various types of memory modules (RAM, ROM, EEPROM, etc.), I/O ports, timers/counters, communication ports, etc. The PIC is based on the Harvard Computing architecture, where code and data are placed in separate registers to increase input/output (I/O) throughout.
In order to make a PIC behave in a desired manner a program must be produced, this is then loaded onto the chip which is then embedded into the desired application.
Some of the applications for PICs include:
- Children’s toys
- Medical equipment
- Telecommunication devices
- Washing machines/ tumble dryers
- Digital boxes
- Remote controls
Image source: http://boingboing.net
PICs are relatively cheap and are widely available, which makes this type of microcontroller increasingly popular amongst hobbyists. Another advantage to PICs is that there is a large quantity of free material readily available to programme these, including software, and as they use flash memory they can be reprogrammed easily making these highly desirable for rapid prototyping.
As mentioned previously, the PIC microcontroller uses Harvard architecture. In this architecture, the program and data are accessed from separate memories so the device has a program memory bus and a data memory bus. This improves the bandwidth over traditional von Neumann architecture where program and data are fetched from the same memory and are accesses over the same bus — separating program and data memory further allows instructions to be sized differently than the 8-bit wide data word.
Image source: https://www.edgefx.in
Pros & Cons
PICs can be used in many different applications, however the suitability of these is completely dependent upon the application. Below are some of the advantages and disadvantages of PICs.
- Peripheral Interface Controllers have only one accumulator.
- Small instruction set.
- Register banking switch required to access RAM of other devices.
- Operations and registers are not orthogonal.
- Program memory is not accessible.
- Reliability — The PIC controlled system often resides machines that are expected to run continuously for many years without any error and in some cases, recover by themselves if an error occurs with help of supporting firmware.
- Performance — Many of the PIC based embedded system use a simple pipelined RISC processor for computation and most of them provide on-chip SRAM for data storage to improve the performance.
- Power consumption — A PIC controlled system operates with minimal power consumption without sacrificing performance. Power consumption can be reduced by independently and dynamically controlling multiple power platforms.
- Memory — Most of the PIC based systems are memory expandable and will help in easily adding more and more memory according to the usage and type of application. In small applications, the inbuilt memory can be used.
- Available in DIL and SMT packages.
- Wide range of interfaces including I²C, SPI, USB, USART, A/D, programmable comparators, PWM, LIN, CAN, PSP, and Ethernet
Summarising the main differences between a PIC and PLC — a PIC is a microcontroller, these are designed for very specific processes. A PLC is a finished product designed for industrial signals which can be used for many different processes and may consist of several microcontrollers. The deciding factor on whether a PIC or PLC would be best suited is usually entirely dependant upon the application.
Towards the middle of the month we had Easter, while to most this would be an excuse to eat generous amounts of chocolate, for me this was a great opportunity to take advantage of some free time. In addition to some well deserved relaxing my fiancé and I took the opportunity trip off since the weather was unexpectedly nice for Yorkshire.
Some of the places we visited include:
Fountains Abbey and Studley Royal
If you enjoy walking this is a fantastic place to visit! Fountains abbey is one of the largest and best preserved ruined Cistercian monasteries in England located in North Yorkshire, and even though what remains of it are ruins the architecture is still incredibly impressive.
From the abbey you can take a walk round to the French inspired Georgian water gardens which really are a beautiful sight.
Cannon Hall farm is a great day out for the family, even without kids we loved visiting here to go and see all the animals! From sheep and pigs to cows and goats spring has to be the best time to visit when all the baby animals are arriving.
I Scream, You Scream...
On a nice day Charlotte’s Ice cream parlour is the place to be where I grew up. There’s nothing like a cold ice cream and visiting the farm animals on a sunny day !
I’m not sure if I missed my calling given my not-so-secret love of visiting farm animals… Maybe I can come up with a way to continue electronic engineering while being surrounded by goats.
While the Easter break felt well deserved it’s definitely nice to be back into the swing of things again. I’m very excited to finish my HND course but at the same time it will be quite nerve racking moving to another university to top-up my HND to a degree. With many more exciting things planned over the coming months I’m sure September will be here in no time!