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.

Only the 600XL and 800XL computers had a PBI. XE systems came with the Enhanced Cartridge Interface (ECI), a functionally similar connection.

Details

During coldstart, the Atari OS polls for parallel bus devices. If found, it'll load handler (aka driver) information into its handler table and initializes the parallel bus device, if needed. The device can utilize the Generic Parallel Device Handler that's already provided once the address is loaded into the handler table.

The device connected to the parallel bus gets its ROM space mapped to the OS Floating-point package subroutines and tables. While the device is selected, no floating-point operations can take place. Once de-selected, the floating-point routines are restored.

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 MIO Board - Hooked up to either a PBI or ECI connection. Featured a RAMdisk, a parallel port, a serial port 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.

See Also

• Enhanced Cartridge Interface (ECI)

References

• Chadwick, Ian (1985). Mapping the Atari Revised Edition. COMPUTE! Publications, Inc. ISBN 0-87455-004-1. [1]