Graphical Displays with PBP3

[rocket_troy]

most likely, the displays have two screen memory regions one for graphics the other for the normal lcd character display
at power up display is in lcd mode, the init routine sets it to graphics, lcds are slow to powerup they cannot be hurried.
if the display is written to before graphics mode is established then its possible some lcd chrs will be displayed accidently.
lcd chrs can only be cleared if the display is in lcd mode , graphic pixels can only be set in graphics mode
both memories are visible on screen no matter what mode is set.

Yeah, what you've said does make sense. I've played around with all sorts of timings - like up to 10s pause after calling the st7920_init and 2s prior, but I don't think it's my writing to the display that's causing the issue as the signs are already there when I call st7920_init.

So, are you aware of any commands I can call to initialise the "character" memory before calling st7920_init?

Thanks,

Troy

[richard]

as in my demo

    Pause  1500      ' LCD initialize time
    lcdout $FE,1
    gosub st7920_init    'graphic mode

[rocket_troy]

[mega facepalm] DUH!!!

Thanks Richard.

Troy

[rocket_troy]

Well, the zeros are still appearing even with up to 5 consecutive commands to clear the character memory. However, probably not as often. Definitely is text in the character display memory that's causing it - no doubt about it, but I'm also sure I'm doing something wrong with either the wiring or initialisation. Probably tolerable for now.

Troy

[richard]

at one stage i did init like this

st7920_init:
lcdout $FE,$24 'In same instruction cannot alter DL, RE and G at once. Make sure that change DL or G first and then RE.
Pause 5
lcdout $FE,$26
Pause 5
bgcolour = 0
colour = 1
return


also look at defines' these may need a fiddle if you display is slower than mine
DEFINE LCD_COMMANDUS 1000 'defines the delay after LCDOUT statement DEFINE LCD_DATAUS 40 'delay in micro seconds


ps i changed to serial mode, perhaps thats why , i forget

[rocket_troy]

at one stage i did init like this

st7920_init:
lcdout $FE,$24 'In same instruction cannot alter DL, RE and G at once. Make sure that change DL or G first and then RE.
Pause 5
lcdout $FE,$26
Pause 5
bgcolour = 0
colour = 1
return


also look at defines' these may need a fiddle if you display is slower than mine
DEFINE LCD_COMMANDUS 1000 'defines the delay after LCDOUT statement DEFINE LCD_DATAUS 40 'delay in micro seconds


ps i changed to serial mode, perhaps thats why , i forget

No luck. Maybe 1 in 10 starts I still get the zeros. Tried increasing the DEFINE LCD_COMMANDUS 1000 to 1500 and DEFINE LCD_DATAUS to 100 and inserted the code you suggested. I didn't mention I need to call the graphic mode initialisation routine a few times to get a reasonably reliable initialisation which might trigger alarm bells? So, my hunch is the display might be slightly different or my wiring is missing something: I've wired up RS, E, RW and the 4 high bits of the data bus and 5V rails. I can't think of anything else?

Troy

[richard]

does it make a difference if you power it down verses a reset >\?

also if you look at the data sheet you can see what commands are needed to make a routine to revert to lcd mode, do a clear screen then return to graphics mode