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

MOS Technology 6502

The MOS Technology 6502 is an 8-bit microprocessor that was designed by Chuck Peddle and Bill Mensch for MOS Technology in 1975. When it was introduced, it was the least expensive full-featured microprocessor on the market by a considerable margin, costing less than one-sixth the price of...

 CPU. The 600XL and 800XL computers, along with the unreleased 1400XL and 1450XLD had a PBI interface. The 130XE system came with the Enhanced Cartridge Interface (ECI), a functionally similar connection.

Details

The PBI is implemented as a rectangular 50-pin edge connector

Edge connector

An edge connector is the portion of a printed circuit board consisting of traces leading to the edge of the board that are intended to plug into a matching socket. The edge connector is a money-saving device because it only requires a single discrete female connector , and they also tend to be...

 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

ROM cartridge

A ROM cartridge, sometimes referred to as a cart, is a removable enclosure containing read-only memory devices designed to be connected to a computer or games console....

 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. Never released.

• ICD Multi I/O Board - Hooked up to either a PBI or ECI connection. Featured a RAMdisk
  RAM disk
  A RAM disk or RAM drive is a block of RAM that a computer's software is treating as if the memory were a disk drive...
  
  , parallel port, serial port, print spooler
  Spooling
  In computer science, spool refers to the process of placing data in a temporary working area for another program to process. The most common use is in writing files on a magnetic tape or disk and entering them in the work queue for another process. Spooling is useful because devices access data at...
  
   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 (http://drac030.krap.pl/en-kmkjz-info.php)

External links

• ICD Boosts 8-bit Atari Power Antic Magazine
  ANTIC (magazine)
  Antic was the name of a home computer magazine devoted to the Atari 8-bit computer line . Its ISSN is 0113-1141. It took its name from the ANTIC chip, which produced the Atari line's graphics. The first issue was published in April 1982. While it began as a bimonthly magazine, within a year it had...
  
  . Review on ICD products for the Atari.