A_OLDSCR

Syntax A_OLDSCR
Location ATARI_REXT (v2.27+)

A lot of software (mainly non-pointer driver programs), and some of the toolkits covered by this book, written for the Sinclair QL in the past always assumed that the QL screen would appear at the memory location 131072 ($20000 in hexadecimal).

These programs and toolkits will not work properly (if at all) on the QVME board or some higher resolution screens. One of the solutions to this is to use the command A_OLDSCR which forces ST/QL Emulators to set up a Job copying the QL’s screen as stored at 131072 (onwards) to the real display screen 20 times a second. This obviously slows down the operation of the computer and thus if possible, a new version of the software should be produced / obtained.

As from v2.30, this command will not affect the display speed as much on a machine fitted with a blitter chip.

NOTE 1

This command cannot fix the problem with programs and toolkits which assume that the QL’s display is 512x256 pixels.

NOTE 2

This command reports ‘Not Implemented’ on other ST-QL Emulators.

NOTE 3

SuperBasic (Job 0) must be the only Job running on the machine when this command is issued, otherwise the error ‘Not Complete’ is reported.

NOTE 4

If you try to use this command after it has already been issued, the errror ‘Already Exists’ is reported.

CROSS-REFERENCE

SCREEN can be used to find the screen address.

SCR_SIZE can be used to set the resolution of the display - much software will insist that this is set to 512x256 pixels also.