little mistery on a hd44780 compatible LCD

[blisca]

Hi to all

At power up i am often stuck with black squares on a varitronix LCD
display, that i use just for test in place of a Powertip LCD(that i have not
in this moment).
No software delay looks able to fix the problem.


touching the ENA pin(commonly pin 6),or connecting it to GND through 1 MOhm
solves completely the problem
Why?
This pin is driven by the RA0 output of a PIC16f628 ,that being a CMOS
output should not need any external pull up or pull down.
The initialization is done following the sequence on data sheet,in 4 bit
mode,and i write checkin the busy flag.

Thank you!
Diego.

 

[Ben Jackson]

touching the ENA pin(commonly pin 6),or connecting it to GND through 1 MOhm
solves completely the problem
Why?
This pin is driven by the RA0 output of a PIC16f628 ,that being a CMOS
output should not need any external pull up or pull down.

Probably you have left RA0 in its default analog mode. All PIC pins
that have analog capabilities come up in analog mode, just because
you might have an arbitrary voltage connected. Even though analog mode
is usually not what you want.

In the case of the 16F628, it's the analog comparator. From some source
of mine, I think you want:

movlw b'00000111' ; comparator off
movwf CMCON

Other PIC chips will have other analog devices you will want to turn off
if you're using all digital.

 

[blisca]

Probably you have left RA0 in its default analog mode. All PIC pins
that have analog capabilities come up in analog mode, just because
you might have an arbitrary voltage connected. Even though analog mode
is usually not what you want.

In the case of the 16F628, it's the analog comparator. From some source
of mine, I think you want:

movlw b'00000111' ; comparator off
movwf CMCON

Other PIC chips will have other analog devices you will want to turn off
if you're using all digital.

I did it exactly in this way,but thanks

being the cable( about 3.1 inches long) the main difference with the
original model i'm thinking to a ringing or something loike this,but sadly i
dont have a digital scope in this moment

thanks again