[V9990] Q&A Official Thread

Hi everyone,

I'm not sure what is wrong ... Trying to fill some VRAM area with zeros, in P1 or B1 mode, but the result is incomplete (parts are not modified). For example, in B1, half of the screen is not cleared.

clear_screen:
	ld	bc,0:32		; P1: 64x64(patterns)x2 = 256x32 values
	dec	d
	jr	c,.go
	ld	bc,0:64		; P2: 128x64(patterns)x2 = 256x64 values
	dec	d
	jr	c,.go
	ld	bc,0:212	; B1: 256x212 values

.go	call	write		; sets VRAM address
	ld	a,e		; 'e' contains value to fill
.loop	out	(v9990.vram),a
	djnz	$-2
	dec	c
	jr	nz,.loop
	ret

Nope, this is the first thing I checked.
R#6 value is 82h, so DSPM=2 (bitmap mode), XIMM=0 (256 pixels width) and CLRM=2 (8 bits/dot)

This is what I get, after writing 256x212 zeros in B1 mode:

Another question: in P1 mode, is it possible to use commands in the pattern name table ?
Its address would translate into (0,3968) and R#38/39 (DY) can contain an Y adress up to 4095 ...

Indeed, GhostWriterP helped me to get the commands working for P1 on the pattern name table. Biggest take away for me was that these are both located on screen "B". As mentioned, a couple of posts back there is an example (which needed the last addition as suggested by GhostWriterP for R37 and R45, R46 and R47).

Sofar I never experienced any problems without waits, not even on r800!