Microcontrollers and YOU!

I figured it'd be a good time to move to a more capable microcontroller as the projects on the blog seems to be getting more and more complicated and lets face it, keeping up with our PIC16 and their limitations can get a little annoying when you're moving lots of important data. We need more pins, we need more features on the chip and we need better instructions.

Enter the PIC18 series from microchip.

http://www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=2696&param=en537796

The PIC18 is the most high end 8-bit microcontroller that microchip offers. It has many advantages over the lower end PIC16s the biggest being a new and improved instruction-set and memory management system.

I suggest you take a look at a datasheet for a PIC, everything in this article will reference:

http://ww1.microchip.com/downloads/en/DeviceDoc/39605F.pdf

A new memory system:

The coolest thing with the PIC18s is an Access Bank system. In this system the MCUs RAM is divided up into 16 banks (0-15)> Each bank has however many memory addresses(Depending on PIC, for example the PIC18F1220 has 256 byte banks) and you select which bank you want with the BSR (Bank Select Register). This sounds awfully similar to ram-pages of the PIC16F however its the access bank delimiter in the opcode that makes life so much easier. The access bank is the first 128 Bytes of bank 0 (Our General purpose registers) and the last 128 of bank 15 (Our Special Function registers) by default all operations are done in the access bank (a=0)This allows us to access a good amount of GPR and all of our SFR without ever changing what bank were working in. No more STATUS,RPx calls. However if we want to access ram outside the access bank we have to set the access bank delimiter call in the instruction to 1 and then by default you will be working in whatever bank happens to be set in the BSR.

Software accessible Stack:

I'm not too familiar with this feature, but the PIC18 allows you to control the stack from software, you also have complete control over the stack pointer, this is extremely powerful and not offered on the PIC16

New and improved modules:

The PIC18 series features an 8-bit hardware multiplier. Microchip provides sample code for doing all sorts of fun arithmetic. This is good if you want to crunch numbers but don't want to go into a full DSP. Also some PIC18s feature on chip USB and other goodies.

Priority interrupts:

This is another really cool feature. The PIC18 features two interrupt vectors, one high priority and one low priority. This allows you to have a really complex interrupt scheme allowing really sophisticated user interaction. For every interrupt you can choose what priority it is. An example of this is having a sample system for a sensor have highest priority while the user interface is low priority, that way even if the user is interacting the device to cause an interrupt, you don't interrupt the sample of the sensor if it is time sensitive.

NEW INSTRUCTIONS!:

This feature is going to take me the longest to get used to, but the PIC18 features a plethora of new instructions to make our lives easier. One nice and needed one is a MOVFF instruction (move from one register to another) These instructions are meant to speed up your code and make execution much faster. All new instructions follow a similar style to the traditional ones, they just do more for the clock. You can take a look at them on page 193 of the datasheet.

Free C compiler:

Microchip offers a free c-compiler for the PIC18 series for MPLAB, i haven't used it but its free and its a c compiler.

Tons of other stuff i still have to figure out:
I'm working on it :P

The PIC18 series is a really powerful line and there isn't much that they cant do. The first project i will be posting with them is a Digitial Audio Processor, we'll be taking advantage of the priority interrupts to make really fast and efficient code.

Hope to see you soon, happy programming!