Graphic LCD

hemnath · Joined: 03 Oct 2012 Posts: 242 Location: chennai

I'm using PIC18F2520, Internal oscillator: 1MHz trying to interface with Graphic LCD: EA DOGM128W-6 (128 x 64 DOTS).

Below is the sample program:

Ttelmah · Joined: 11 Mar 2010 Posts: 19552

Realistically, increase the oscillator frequency.
Remember there is nothing to stop you changing it 'up' for the graphics, and then back down as soon as you have finished drawing.
Problem is the sheer amount of data involved when dealing with a graphics screen.....

temtronic · Posted: Tue Jul 25, 2017 4:48 am

I have to agree with Mr. T !

Not only will it be very,very slow when using the graphics module but everything else lke serial I/O, SPI, I2C, etc. Even 'math' routines will be painfully slow.

Is there a specific need to run that powerful PIC at only 1MHz?

Jay

hemnath · Joined: 03 Oct 2012 Posts: 242 Location: chennai

I have to save the current consumption since it is battery operated :(

I thought my logic will be slow in displaying the value since I am not an expert. Need your help guys.

temtronic · Posted: Tue Jul 25, 2017 5:29 am

OK, that explains why.....
You should goto Microchip's website, find the 'application notes' section, then download the apnote about 'low power'. It'll be a low numbered apnote, probably 25 years old STILL valid today. They use an 8 pin PIC, A2D and several 'coin cell' batteries for the tests. It's really a 'must read', sorry I don't have my apnotes here,can't give you the #, but it is old....
In it they run PIC at several speeds (sleep, low speed, max,etc) and chart ACTUAL power usage with some surprises !!

Other options for battery powered devices...
Use a bigger battery. I know obvious but today you can get a LOT of power in a small package but you'll ALWAYS get more power in a bigger battery. I use 4 x AA sized batteries (series-parallel for 3V) for remote devices like data loggers.

Add a 'super cap' to your PC project. It'll help smooth the current demands nd prevent brownout resets

Be SURE to set every unused I/O pin to a '1' or '0' to reduce power.
Control the backlight of the LCD with PIC I/O pin.ONLY on when needed.

Also turn off every unused peripheral. ADC, Comp, UART, etc. All these internal peripherals take power, most can be turned off.

Jay

Ttelmah · Joined: 11 Mar 2010 Posts: 19552

Yes.

The key point in that note, is that it often uses more power to clock slowly!.....
Problem is that current consumption is not linear, and the overheads are there all the time.

So (for instance), you have a job that takes 1 second at 1Mhz, or 1/16th second at 16Mhz. The PIC draws perhaps 1uA at 1Mhz, and 10uA at 16MHz. So the power that has to be delivered to do the job at 16MHz, is 10uA*0.0625*3.4 (assuming 3.4v supply) = 2.125uW. At 1MHz, the same job uses 1*1*3.4 = 3.4uW. So it actually draws 1.6* as much power to do the job at the slower rate!.....

Do the job quickly, and then suspend the PIC as much as possible. Perhaps putting it completely to sleep.

Understand that in most programs the chip spends far more of it's time 'doing nothing' (waiting), than anything else. Because this is the largest part of the processor's time, this is where most power can be saved....

hemnath · Joined: 03 Oct 2012 Posts: 242 Location: chennai

Thanks for your valuable comments. I have increased the clock frequency. Now it displays at faster rate.

Below is the routine I used to display the data. It is working good.

Ttelmah · Joined: 11 Mar 2010 Posts: 19552

There are several strange things here:

A two dimensional array, with the first element declared as [1], should only be declared as a one dimensional array.

Why on earth have an array containing just zeros?. This wastes a huge amount of time, when you could get rid of the array accesses completely...

hemnath · Joined: 03 Oct 2012 Posts: 242 Location: chennai

How to write efficiently. Please help.

hemnath · Joined: 03 Oct 2012 Posts: 242 Location: chennai

Facing another problem,

When i used to display like this, it works

oxo · Joined: 13 Nov 2012 Posts: 219 Location: France

Either

Ttelmah · Joined: 11 Mar 2010 Posts: 19552

If you look he is declaring an array. So need %s not %c as well....

%c means 'print one character'. %s is the command to print a 'string' from a character array.

He also needs the compiler directive 'PASS_STRINGS="IN_RAM"', for this to work.

oxo · Joined: 13 Nov 2012 Posts: 219 Location: France

Gotta leave something for the student to do ;)

hemnath · Joined: 03 Oct 2012 Posts: 242 Location: chennai

I tried as,

Ttelmah · Joined: 11 Mar 2010 Posts: 19552

First the syntax only works by fluke....

MENU[0] is the physical element at the first location in the array.

&MENU[0] is the address of this element.
MENU (on it's own), is a C short-cut for this address of this element.

MENU[0] only works because CCS internally automatically turns this into the address, if used in a function expecting an address. This has been commented on before but it means it won't work in other languages, and is not guaranteed to work with future versions....

Then why bother?. Use the compiler #device PASS_STRINGS option.

This automatically does the copy from ROM to RAM for you, and does it using only a tiny buffer. Doing it manually means you have to have a large enough buffer for the whole string. Probably OK for now, but 'long term' as you use larger chips and larger strings, not practical....

The only real reason now to use the strcpy syntax, would be if you are using an old compiler (PASS_STRINGS has worked well now for many dozens of versions).

A search here will find the explanation of 'why' you have to do one or the other.