Hi!

Execution times for LCD are:

        clear display:          82microseconds - 1.64ms (you put  space char into each
display address)
        display&cursor home:    40micro - 1.64ms

First two commands have variable execution times. You should also wait 10-15
ms after power up for full initialisation sequence of LCD.

        character entry mode:   40micro
        display on/off & cursor:        40micro
        display/cursor shift:   40micro
        function set:           40micro
        set cgram address:      40micro
        set display address:    40micro
        write data:             40micro
        read data:              40micro
        read status:            1micro

You have 6,25ms time, so displaying 20 characters  shouldn't be any problem
even with fixed delays, but the fastest way would probably be by checking
LCD's busy flag. Regards, Samo

-----Original Message-----
From: pic microcontroller discussion list [mailto:PICLIST@MITVMA.MIT.EDU]On
Behalf Of David Queen
Sent: Sunday, May 13, 2001 10:23 PM
To: PICLIST@MITVMA.MIT.EDU
Subject: [PIC]: Time needed to display on a LCD?


I am just starting to lay out the basics of a project and I am not sure of
how fast you can write to a LCD display.

I am going to use a 16F877 at 20mhz and a 4bit interface.

If things go as planed I hope to have an interrupt every 1/160 second.
That should give me about 31,000 instructions to get some work done.
The interrupt will set a byte and then return to the main loop.
Each task will then have to finish in no more than 1/160 second.

I will need to be to write a 20 char line to the display whit in that time.
Is it possible?

Also anyone see a major problem with this kind of loop tasking?
I am hope it works, it will let me break the project down into smaller parts
to debug.

main loop         nop
                       if task =0 call0
                                ****
                       if task=15 call15
busywait          if task = same_as_last_Time goto busywait



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