SYSTEMS GUIDE

Memory Map: Page 2 Continued

by James Capparell

Memory Map is an on-going feature of ANTIC. See issue #1, 2, and 3 for previous installments. We intend to publish the function of all the low memory RAM locations. The format for our description is:

12 $C 2 DOSINI

The Operating System variable called DOSINI uses 2 continguous locations starting at address 12 (decimal) or C (hexidecimal).

Page 2 continued

673 $2A1 1 TMPLBT

??

674 $2A2 1 ESCFLG

Used by screen editor. Flag set to $80 when ESC [$1B] character detected. Reset to 0 following output of next character. Causes character following ESC to be displayed. Only exception is EOL [$9B].

675 $2A3 15 TABMAP

Logical Line start.

690 $2B2 4 LOGMAP

Logical line bitmap. When a bit is set then a logical line starts at the corresponding physical row number. All bits set to 1 when text screen is opened or cleared.

694 $2B6 1 INVFLG

Inverse video flag toggled by ATARI logo key sets bit 7 = 1.

695 $2B7 1 FILFLG

Indicates to display handler whether current operation is fill <> 0 or draw = 0.

696 $2B9 1 TMPROW

??

697 $2B9 2 TMPCOL

??

699 $2BB 1 SCRFLG

Scroll flag set to number of physical lines - 1 that were deleted from top of screen. Since logical lines range from 1-3 physical lines then this variable ranges from 0-2.

700 $2BC 1 HOLD4

Used to save and restore value in ATACHR [$2FB] during fill process when ATACHR is temporarily set to value in FILDAT [$2FD].

701 $2BD 1 HOLD5

Temporary used by draw.

702 $2BE 1 SHFLOK

Shift/control lock flag initialized to $40 at powerup.
$00 = normal mode lowercase alpha $61-$7A
$40 = caps lock upper case $41-$5A
$80 = control lock $01-$1A

703 $2BF 1 BOTSCR

Bottom of screen = 4 then mixed mode, = 24 then normal.

704 $2C0 4 PCOLR0-PCOLR3

Player color registers and shadows.
PCOLR0 = COLPM0 [$D012]
PCOLR1 = COLPM1 [$D013]
PCOLR2 = COLPM2 [$D014]
PCOLR3 = COLPM3 [$D015]

708 $2C4 5 COLOR0-COLOR3

Playfield color registers and shadows.
COLOR0 = COLPF0 [$D016]
COLOR1 = COLPF1 [$D017]
COLOR2 = COLPF2 [$D018]
COLOR3 = COLPF3 [$D019]
COLOR4 = COLBK [$D01A]

713 $2C9 23 SPARE

**

736 $2E0 2 GLBABS

Contains entry address of code for auto-boot/run.

738 $2E1 2 SPARE

**

740 $2E4 1 RAMSIZ

Size in pages of available RAM permanently retains RAM top address contained in TRAMSZ [$6] with BASIC and 48k the = $160 = 40960.

741 $2E5 2 MEMTOP

Top of available user memory RAMSIZ less display list and display memory (first nonuseable address). This value established by powerup logic and reset re-established when screen display is opened.

743 $2E7 2 MEMLO

Bottom of available user memory established at powerup and reset, not altered after that.

745 $2E9 1 SPARE

**

746 $2EA 4 DVSTAT

Device status buffer. Get status command puts information in these bytes.

750 $2EE 1 CBAUDL

Cassette baud rate low byte.

751 $2EF 1 CBAUDH

Cassette baud rate high byte.

752 $2F0 1 CRSINH

Cursor inhibit flag. If = 0 then cursor on. If > 0 then no visible cursor.

753 $2F1 1 KEYDEL

Key delay set to 3 whenever key code acepted. Decremented every 1/60 sec by stage 2 VBLANK process until it reaches 0.

754 $2F2 1 CHI

Prior key code read and acepted. Current key pressed compared with contents of CH1 if same then debounce time checked. If OK then accepted. If current key not same as CH1 then accepted. When accepted stored in CH [$2FC].

755 $2F3 1 CHACT

Shadow for CHACTL [$D401] char control register.
bit 2 = 1 causes current character line to invert sampled at every char. line.
bit 1 = 2 in 40 char. mode if bit 7 of current char. code = 1 then char is blue on white
bit 0 = 1 in 40 char. mode if bit 7 of current char. code = 1 then car. will be black blinking char produced by setting bit 7 of char. and periodically changing bit 0 here.

756 $2F4 1 CHBAS

Vector to page address of character set init's to E0 (upper case and punctuation) char set in ROM is $E000-E3FF shadow for CHBASE [$D409].

757 $2F5 5 SPARE

**

762 $2FA 1 CHAR

Contains internal code corresponding to what is in ATACHR [$2FB]. This will be converted to ATASCII.

763 $2FB 1 ATACHR

ATASCII character for most recent char read or written or value of the graphics point. This value also determines color of line in draw and fill commands.

764 $2FC 1 CH

Holds keyboard code for a character (not ATASCII). Keyboard handler gets all data from here when it gets a character. It writes $FF here to indicate code read. This location loaded when a key is pressed causing an IRQ interrupt which vectors at $208. This interrupt service routine loads the code into $2FC for processing at VBLANK stage 2.

765 $2FD 1 FILDAT

Right fill data for draw.

766 $2FE 1 DSPFLG

Display flag will allow control codes other than EOL [$98] to be displayed if flag <> 0. If flag = 0 then control codes processed normally.

767 $2FF 1 SSFLAG

Start/stop flag toggled by control-1 keys cleared by break key, reset key, or powerup.

Page 3

DCB--Device Control Block
Used for hanler/SIO communication and between user and disk handler.

768 $300 1 DDEVIC

Peripheral unit 1 bus I.D. number.

769 $301 1 DUNIT

Unit number.

770 $302 1 DCOMND

Bus command.

771 $303 1 DSTATS

Command type status return.

772 $304 2 DBUFLO

Data buffer pointer. Set by handler to indicate source or destination data buffer.

To be continued in another issue