Posted By
Litwr
on 2022-07-03
15:27:29
|  Is there any use of TED registers 1A and 1B?
Does anybody know how get something useful from these registers? They are connected to two internal pointers to the actual character position. But it seems, we can't change the internal pointers via 1A/1B. If we write there it doesn't affect the internal registers.  Or I missed something?
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Posted By
Csabo
on 2022-07-03
15:34:32
| Re: Is there any use of TED registers 1A and 1B?
The encyclopedia has a brief description of those two. They can be used for scrolling the bitmap screen, e.g. many old demos would use this to implement a logo-mover effect while playing digi (since it's so "cheap", as in it doesn't take too much raster time). Does this help?
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Posted By
siz
on 2022-07-03
16:07:50
| Re: Is there any use of TED registers 1A and 1B?
Or I missed something?
It is updated by the TED once in every "character" row. If you want to move the bitmap you have to set it in every frame. (Moving the bitmap = setting the start address for the next character row)
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Posted By
Litwr
on 2022-07-04
03:03:51
| Re: Is there any use of TED registers 1A and 1B?
>The encyclopedia has a brief description of those two.
IMHO our encyclopedia is not correct. These TED registers are not "Current character-position"! The current character-position is an internal TED register, we don't have the direct access to it.
Let's examine the next my code.
org $1001
byte $b,$10,$a,0,$9e,"4128",0,0,0
org $1020
SEI
STA $FF3F
LDX #$1B
STX $FF06
LDA #>irqe1
STA $FFFF
LDA # STA $FFFE
LDA #$1C ;irq at line $1C = 28
STA $FF0B
LDA #$A2 ;0 - hi byte, raster irq only
STA $FF0A
CLI
loo: jmp loo
irqe1 PHA
inc $ff19 ;make the green line, stage 1
LDA #0
STA $FF1B ;reset the character reload position
STA $FF1A ;it has no any effect
PLA
INC $FF09
dec $ff19 ;make the green line, stage 2
RTI
It produces the next picture
- there is no any effect of changing of 1a/1b. Someone may expect that the initial lines should be repeated after the green line...
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Posted By
siz
on 2022-07-04
06:52:13
| Re: Is there any use of TED registers 1A and 1B?
The change works in bitmap mode only.
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Posted By
Csabo
on 2022-07-04
08:31:33
| Re: Is there any use of TED registers 1A and 1B?
As siz said, but there's one thing I'd like to add:
If you want to take a look at some programs that use these registers, try TLC's First Demo (TLC) (a criminally underrated production IMHO), the 4th part with two logos swinging, or perhaps Uncertain Future (the part with the buildings).
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Posted By
Litwr
on 2022-07-04
14:02:20
| Re: Is there any use of TED registers 1A and 1B?
>The change works in bitmap mode only.
Thank you very much. It actually works! However it is sad that all known to me documentation has still missed this important information.
It is interesting that in text modes those registers are updated too but in fact they are not used.
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Posted By
Csabo
on 2022-07-04
14:20:14
| Re: Is there any use of TED registers 1A and 1B?
Good point! I updated the encyclopedia with this note.
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Posted By
Gaia
on 2022-07-04
19:25:29
| Re: Is there any use of TED registers 1A and 1B?
The cursor counter is compared to this register, too, so you can actually move the cursor around by modifying it in text mode. Normally it is not visible, though, when running programs of course.
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