APPENDIX ELEVEN



     To recall the screen, use the same USR routine and the above
     PEEKs and POKEs, but POKE 898,7 rather than 11. This was de-
     rived from a larger program by Fred Pinto in the March 1984 is-
     sue of Antic. An article by Steve Kaufman in COMPUTE!,
     November 1983, has a fast and dirty method which works just
     as well (save and load), but doesn't save the color registers.
     Creative Computing, November 1983, also had a similar ex-
     ample in "Outpost Atari."

106            6A             RAMTOP
     See K.W. Harm's article on the "RAMTOP Dragon" in COM-
     PUTE!'s Second Book of Atari Graphics to see how to protect
     high memory; another article in the same book, by Jim Clark.
     describes how to protect low memory.

118            76             DELTAR
     This is the change of vertical position when drawing a sloped
     line.

121            79             ROWINC
     Direction of line draw: 0 is down, 255 is up.

122            7A             COLINC
     Direction of draw: 0 is right, 255 is left.

126,127        7E,7F          COUNTR
     Iterations or steps required to draw a line.

132,133        84,85          VNTD
     COMPUTE!, October 1983, has an article by E.H. Foerster on
     how to reserve a portion of RAM above VNTD--within a BASIC
     program--which will also be saved intact when you save the
     program.

138,139        8A,8B          STMCUR
     Another way to lock up the system if something is done--say,
     BREAK pressed--is by Z=USR(0).

146            92             MEOLFLG
     BASIC's modified EOL flag register. The Atari BASIC Sourcebook
     lists all the RAM locations used by BASIC (pages 144-147).

147            93             ....
     Spare.

149,150        95,96          POKADR
     Address (LSB/MSB) of last POKE location, If no POKE command
     was given, it is the address of the last OPERATOR token (often
     155 for EOL).