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...
|
