CTRL register's Character Width bit

[ArcadeAction]

Hello,

Now that I have a concrete idea for a relatively small game that I would like to play on the 7800 (way too early to reveal,
I'd hate to end up on Trebor's Atari 7800 Homebrews and Hacks Thread "dormant" list ), I've picked up 7800 programming again.

To see if I can wrap my head against MARIA's indirect character mode, I'm trying to hack Dan Boris' sprite demo code into a tiled mode demo (without sprites).

The 7800 programmer's guide says this (I've checked two versions):

The CTRL register is arranged as follows:
CK | DM1 | DM0 | CW | BC | KM | RM1 | RM0

...
CW - Character Width.
0 => Two (2) byte characters.
1 => Single byte characters.
...

 

When I setup the CTRL register with CW=1 (Single byte character):

	lda	#%01010011
	sta	CTRL

I get the (unexpected) output as attached (7800_cw_1.png)

While when I set it CW=0 (Two (2) byte characters), I get the output that I hoped to see, three smileys next to each other (7800_cw_0.png).

 

But don't understand why CW=0 works, I had expected CW=1 to produce the right result.

 

This is how I setup CHARBASE

	lda #$a0
	sta CHARBASE

Here's the relevant DL entry (xpos is contant with 0 value):

   	;Create DL entry for background
   	
   	ldy	dlend,x		;Get the index to the end of this DL
   	lda	#$00				
	sta     (dlpnt),y	;Low byte of data address
	iny
	lda	#%01100000	;Mode 320x1
	sta     (dlpnt),y
	iny 
	lda	#$b0
	sta     (dlpnt),y
	iny
	lda	#%00011101	;Palette 0, 1 byte wide
	sta     (dlpnt),y
	iny
	lda	xpos		;Horizontal position
        sta     (dlpnt),y
        sty	dlend,x

And this is the graphic data and the tile data:

;************** Graphic Data *****************************
        org $a000
        .byte     %00111100
        org $a100
        .byte     %00111100
        org $a200
        .byte     %01000010 
        org $a300
        .byte     %01000010 
        org $a400
        .byte     %10011001
        org $a500
        .byte     %10011001
        org $a600
        .byte     %10100101
        org $a700
        .byte     %10100101
        org $a800
        .byte     %10000001
        org $a900
        .byte     %10000001
        org $aA00
        .byte     %10100101
        org $aB00
        .byte     %10100101
        org $aC00
        .byte     %01000010
        org $aD00
        .byte     %01000010
        org $aE00
        .byte     %00111100
        org $aF00
        .byte     %00111100

;************** Character map *****************************

		org $b000
		.byte $0,$0,$0

Can somebody explain why two tiles are updated, while I tell the Maria chip that one character takes up 1 byte?

 

I have added my modified script, but it's an experiment and messy, as I left a lot of the original code of Dan Boris' sprite code in it.That's fully my fault, do not blame Dan for this

Thanks in advance for any help!

background_test.asm

atari7800.asm

Edited April 30, 2017 by ArcadeAction

[Mord]

I remember there's some sources with typos compared to the original gcc maria docs. I think this is one of them.

 

In the attached doc it states the opposite of some other maria.txt files I have for the CTRL register's character width.

 

 

 

 

gcc1702b_maria_specs.pdf

[RevEng]

Mord is correct, 0=single width, 1=double width. The wiki version of the guide had this error too, but I've corrected it now.

[ArcadeAction]

Great, thank you. I concluded the same after some more testing on my part (with a map with more characters)