Blackboard buffer
Whenever a blackboard's state needs to be examined or updated, its buffer is copied to the addresses in page 0 shown below by the routine at $1421. Afterwards, the blackboard's buffer is restored from page 0 by the routine at $1445.
Address Length Description
$0019 $01
Blackboard pixel column counter
Used by the routines at $1129, $11CF and $16E9.
$001A $01
Number of the character who last wrote on the blackboard
Used by the routines at $0A58, $1129, $16E9, $176F, $19A5 and $1FA0.
$00DF $04
Last four bytes of the blackboard's buffer
Used by the routines at $176F, $184E, $19A5 and $1FA0.