Call Box Commands
Version 2.0 15 Jan-90


CALL SB the SCAN LINE CONTROL BYTE commands

There are 2 commands that control the Scan line Control Bytes (SCB's). A Scan line Control Byte describes the behavior of the pixels for each row of the screen. The screen has 200 rows of pixels that can be either 320 or 640 pixels wide depending on the mode setting.

Figure 2.14
Figure 2.14 Scan Line Control Byte

Binary is a convienient method to specify scan line control bytes. To set all 200 SCB's to 640 mode graphics use the following program line:

CALL SB,0,!10000000,0,200

You will usually use palette 0 for all of your needs even though there are 16 palette spots avaliable. It should be noted that specifying a palette that has not been filled by a CALL PL will produce unpredictable results.


COMMAND FUNCTION DESCRIPTION
CALL SB,0,(scb),(start),(end) SET RANGE OF SCB's: Sets any or all of the 200 scan line control bytes associated with the screen.
CALL SB,1,(line),R GET ONE SCB VALUE: Returns the value of a specified SCB.


(scb)
A value as described in Figure 2.14.

(start)
Top row of the range of SCB's to be set.

(end)
Bottom row of the range of SCB's to be set.

(line)
Line number of SCB to read.

R
Returned value ... must be an Applesoft FP (real) variable.