Parallel Bus Interface Explained

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 Ground2 External select
3 A0 Address output4 A1
5 A26 A3
7 A48 A5
9 A610 GND
11 A712 A8
13 A914 A10
15 A1116 A12
17 A1318 A14
19 GND20 A15
21 D0 Data (bidirectional)22 D1
23 D224 D3
25 D426 D5
27 D628 D7
29 GND30 GND
31 Phase 2 clock output32 GND
33 NC Reserved34 Reset output
35 (IRQ) Interrupt request36 Ready input
37 NC38 External decoder output
39 NC40 Refresh output
41 Column address output42 GND
43 MPD Math pack disable input44 Row address strobe
45 GND46 Latch read/write out
47 NC (+5V on 600XL only)48 NC (+5V on 600XL only, used for 1064)
49 Audio input50 GND

Devices

References

External links

Notes and References

  1. Web site: Zrób sobie sam interfejs IDE! - Forum Atarum.
  2. Web site: Ram 320Xl.
  3. Web site: RAM320XE/576 order thread.