Parallel Bus Interface (above) and Enhanced Cartridge Interface (below, with cartridge socket).European 800XL with Parallel Bus Interface visible (above, with cover removed) and 130XE with Enhanced Cartridge Interface (below).
The Parallel Bus Interface, or PBI, is a 50-pin port found on some XL models of the Atari 8-bit computers. It provides unbuffered, direct connection to the system bus lines (address, data, control), running at the same speed as the 6502 CPU. The 600XL and 800XL, along with the unreleased 1400XL and 1450XLD have a PBI interface.
The Enhanced Cartridge Interface, or ECI, is a modified version of the PBI designed to be smaller and less expensive to implement. Many of the pins in the PBI are duplicated in the 30-pin cartridge slot, so ECI was limited to only those 14 pins in the PBI that were not in the cartridge slot. Placed side-by-side on the back of the computer, devices plugged into both at the same time to provide the same electrical interface as the PBI. The ECI is found on late production units of the 65XE, the 130XE, and the 800XE.
Details
The PBI is implemented as a rectangular 50-pin edge connector on the back of XL machines. The pins include all 16 address lines (A0 through A15) and 8 data lines (D0 through D7). Other pins include various electrical supplies, clock signals, interrupts, memory strobes, and even an analog audio input.
As many of these pins were already implemented as part of the already-existing 30-pin ROM cartridge slots on Atari machines, the XE series re-implemented the PBI to include only those pins that the PBI had but the cartridge slot didn't. The resulting connector contained only 14 pins, mostly the address pins A13 though A15, and the various sound and signal pins of the PBI. The ECI slot was placed beside the cartridge slot, allowing a single connector to be inserted into both connectors and re-create the functionality of the entire PBI.
Pinout
Parallel Bus Interface (PBI) - looking at the back
1
3
5
7
9
11
13
15
17
19
21
23
25
27
29
31
33
35
37
39
41
43
45
47
49
2
4
6
8
10
12
14
16
18
20
22
24
26
28
30
32
34
36
38
40
42
44
46
48
50
Parallel Bus Interface (PBI) - Pinout
Pin
TOP
Pin
BOTTOM
1
GND Ground
2
External select
3
A0 Address output
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 Data (bidirectional)
22
D1
23
D2
24
D3
25
D4
26
D5
27
D6
28
D7
29
GND
30
GND
31
Phase 2 clock output
32
GND
33
NC Reserved
34
Reset output
35
(IRQ) Interrupt request
36
Ready input
37
NC
38
External decoder output
39
NC
40
Refresh output
41
Column address output
42
GND
43
MPD Math pack disable input
44
Row address strobe
45
GND
46
Latch read/write out
47
NC (+5V on 600XL only)
48
NC (+5V on 600XL only, used for 1064)
49
Audio input
50
GND
Devices
Atari 1064 Memory Module - Designed specifically for the 600XL, it upgraded the memory of the 600XL to 64kB. Only parallel bus device released by Atari.
Atari 1090 Expansion System - Designed to give expansion slots to the XL computers.
ICD Multi I/O Board - Hooked up to either a PBI or ECI connection. Featured a RAMdisk, parallel port, serial port, print spooler and a hard disk interface.
Black Box - The Black Box by CSS hooks up to either PBI or ECI connection. Featured a SCSI interface, a serial port, parallel port, floppy drive interface and a built-in menu system.
