Most of the Atari 600XL and 800XL models were supplied with the "debugged" version B of Atari BASIC. This new BASIC got rid of the minor bugs of BASIC A and introduced some new major bugs of it's own.
Each time a program is saved, 16 extra bytes are tagged onto the end of the program. After many saves and reloads, as when developing a long program, the program becomes too large for the memory.
The computer may lock up unpredictably.
Program line links may get messed up, leaving garbage in the listing and the program unrunable.
Large LISTed programs may not run unless SAVed and reLOADed.
If the length of a listed program is a multiple of a certain number of bytes, it will not run unless the length is somehow changed.
BASIC version B has been replaced by version C. All of the XE models have this truly debugged version of BASIC.
I have heard of only one bug in the operating system in XL and XE models. This is a mishandling of the printer timeout. The computer cannot tell if there is a printer attached or not. This may have been fixed in the XE models. However, many programs, some even formerly sold by Atari, do not jump through published jump vectors when using the operating system. These programs will not run on XL/XE models. (Some of these programs are Atari Word Processor (not Atariwriter) and LJKs Letter Perfect and Data Perfect.) Since the operating system ROM can be switched to RAM, a "translator" can be used to load the 800 operating system into an XL or XE model.
The 130XE has an extra 64K bank of memory. It is divided into four blocks of 16K each. Each block can be switched to replace part of the main bank of RAM from $4000 (16384) to $7FFF (32767). Furthermore, it can be switched in such a way that only the 6502, or the ANTIC chip can see the extra memory.
Port B (formerly the two extra joystick ports of the 400/800) is used to manage the memory.
Port B and memory management
7 6 5 4 3 2 1 0
-----------------
PORTB |T|U|A|C|S S|B|R|
-----------------
1 6 3 1 8 4 2 1
2 4 2 6
8
R 1 = OS replaced by RAM
B 0 = BASIC enabled
S S bank select bits
C 0 = CPU sees switched RAM at $4000
A 0 = ANTIC sees switched RAM
U unused
T 0 = self test
Bits 2 and 3 of PORTB select which block of the extra bank of memory is switched in.
Bank select bits
bits block
2 3 address
-------------------------
0 0 $0000 - $3FFF
0 1 $4000 - $7FFF
1 0 $8000 - $BFFF
1 1 $C000 - $FFFF
Bits 4 and 5 select which chip sees the switched in RAM at $4000 - $7FFF
Chip select bits
bits ANTIC 6502
4 5
--------------------------
0 0 Ext. Ext.
0 1 Ext. Main
1 0 Main Ext.
1 1 Main Main
Pin out of the parallel port
top from rear
111112222233333444445
2468024680246802468024680
-------------------------
-------------------------
11111222223333344444
1357913579135791357913579
1 2 GND
3 A1 4 A0
5 A3 6 A2
7 A5 8 A4
9 GND 10 A6
11 A8 12 A7
13 A10 14 A9
15 A12 16 A11
17 A14 18 A13
19 A15 20 GND
21 D1 22 D0
23 D3 24 D2
25 D5 26 D4
27 D7 28 D6
29 GND 30 GND
31 GND 32 phase 2 clock
33 RESET 34
35 RDY 36 IRQ
37 37
39 40
41 GND 42
43 RAS 44
45 R/W 46 GND
47 +5V 48 +5V
49 GND 50
The phase 2 clock runs at 1.8 MHz. When the clock is high, the address and R/W lines are valid. The clock goes from high to low, when the data lines are also valid. All lines then become invalid.
The 130XE doesn't have the parallel port. However, it has a cartridge slot expansion. This is a small cartridge-slot-like connector with the necessary connector to use parallel expansion.
If address $026E (622) is $FF, graphics 0 will be in the fine scroll mode.
DSCTLN [$0D25,2 (725)] is the disk sector size. should be $80 (128).
DMASAV [$02DD (735)] is a copy of the DMA control register, SDMCTL [$022F (559)]. It is set up when a channel is opened to the screen. The value is moved to SDMCTL whenever a key is pressed. It is used to restore the display if DMA is disabled.
PUPBT [$033D,3 (829-831)] is used to test memory integrity when [RESET] is pressed. If these bytes are not $5C, $93 and $25, the computer will do a cold start when [RESET] is pressed.
The self-test ROM is from $D000 to $D7FF, the same addresses as the hardware registers. This part of the operating system ROM is disabled when not used. When The computer is put into the self-test mode, This part of ROM is copied to $5000 to $57FF and run from there.
GINTLK [$03FA (1018)] is a logical 1 if a cartridge is installed (built-in BASIC is considered a cartridge). BASIC can be disabled by poking 1018 with a non-zero number. If [RESET] is then pressed, the computer will attempt to load the DUP.SYS file and basic will be completely disabled.