Atari 600XL and Atari 800XL have parallel bus interface. It's said that they are not 100% compatible - 600XL has +5V lines, because 1064 memory expansion module needs power. Also, 1064 and 600XL housing are compatible, but 1064 can't be inserted in 800XL.

1	gnd
2	/EXTSEL	goes low if EXTENB is enabled and selected device uses the address.
3	A0
4	A1
5	A2
6	A3
7	A4
8	A5
9	A6
10	gnd
11	A7
12	A8
13	A9
14	A10
15	A11
16	A12
17	A13
18	A14
19	gnd
20	A15
21	D0
22	D1
23	D2
24	D3
25	D4
26	D5
27	D6
28	D7
29	gnd
30	gnd
31	phi2	buffered phase 2 clock
32	gnd
33	[nc]
34	/RST
35	/IRQ
36	/RDY	slow PBI device can extend the CPU bus cycle by pulling low this line
37	[nc]
38	EXTENB	external decoder enable. Goes high when an address is an allowed address for a PBI device.
39	[nc]
40	/REF	refresh
41	/CAS	column address strobe
42	gnd
43	/MPD	math pack disable. When device is selected and has handler in D800-DFFF
44	/RAS	row address strobe
45	gnd
46	R/W
47	[nc]	+5V on 600XL
48	[nc]	+5V on 600XL
49	audio in
50	gnd

Most XE models have cartridge port at back and instead of PBI they have some lines in so called ECI.

A	reserved
B	/IRQ
C	/HALT
D	A13
E	A14
F	A15
H	gnd
1	/EXTSEL
2	/RST
3	/D1XX
4	/MPD
5	audio in
6	/REF
7	+5V

Back (c) 1998-2004 Jindroush Last modified: Sun Mar 25 23:48:56 2001