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 devices. If found, it'll load handler (aka "device") information into its handler table and initializes the parallel 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 conversion routines from ASCII to Floating-point. While the device is selected, no floating-point operations can take place. Once de-selected, the floating-point routines are restored.

Devices

The only released parallel bus device from Atari was the Atari 1064 RAM Expansion Unit. Designed specifically for the 600XL, it upgraded the memory of the 600XL to 64kB.

Built but never released, the Atari 1090 Expansion Unit was designed to give expansion slots to the XL computers.

See Also

• Enhanced Cartridge Interface (ECI)

References

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