Parallel Bus Interface

The Parallel Bus Interface, or PBI, is a 50-pin port found on some Atari 8-bit XL 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 computers, along with the unreleased 1400XL and 1450XLD had a PBI interface.

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 Enhanced Cartridge Interface, or ECI, was a modified version of the PBI designed to be smaller and less expensive to implement. Many of the pins in the PBI were 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 was found on the 65XE (late production units only), 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
135791113151719212325272931333537394143454749
2468101214161820222426283032343638404244464850
Parallel Bus Interface (PBI) - Pinout
PinTOPPinBOTTOM
1GND Ground 2External select
3A0 Address output 4A1
5A2 6A3
7A4 8A5
9A6 10GND
11A7 12A8
13A9 14A10
15A11 16A12
17A13 18A14
19GND 20A15
21D0 Data (bidirectional) 22D1
23D2 24D3
25D4 26D5
27D6 28D7
29GND 30GND
31Phase 2 clock output 32GND
33NC Reserved 34Reset output
35(IRQ) Interrupt request 36Ready input
37NC 38External decoder output
39NC 40Refresh output
41Column address output 42GND
43MPD Math pack disable input 44Row address strobe
45GND 46Latch read/write out
47NC (+5V on 600XL only) 48NC (+5V on 600XL only, used for 1064)
49Audio input 50GND

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. Never released.
  • 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.
  • SupraDrive - an early SCSI disk drive.
  • Karin Maxi, a parallel floppy disk drive.
  • KMK/JŻ IDE (aka IDEa), an ATA host adapter ().
  • Turbo Freezer XL/XE, a freezer with onboard ROM including a monitor/debugger and RAM expansion (re-released 2005 and 2011 by ABBUC).
  • IDE2ECI[1]
  • RAM320XL for the PBI[2] and RAM320XE/576 for the ECI[3] external RAM expansions.

References

  • Ian Chadwick, Appendix 14: The XL/XE Parallel Bus, Mapping the Atari Revised Edition, COMPUTE! Publications, ISBN 0-87455-004-1
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