PCI & Podules

Peripheral Component Interconnect (PCI) Bus

The new expansion bus for Phoebe, a common standard on PCs, Apple Macs and UNIX workstations.
Implements a 32 bit bus, running at a clock speed of 33MHz.
Four PCI slots are provided, on a riser that attaches to the edge of the motherboard.
The interface between the internal and PCI busses is handled by a PCI Bridge, the PLX Technology 9080.
The PCI Bridge handles the protocol conversion for data travelling to and from the PCI bus
It also arbitrates the Master/Slave relationship between devices on the bus. This allows other devices - a PC card, for example - to temporarily take control of the bus.
It will be possible to use standard PCI cards on this bus. However, drivers will have to be written to allow Phoebe to access them.
Care has been taken in designing the PCI bus to ensure that it is correctly terminated. This is essential of the bus is to run reliably at high speed.
Dave Walker mentioned that a driver for a 3Dfx three-dimensional graphics accelerator is currently in development.
Acorn also expect the PCI bus to be used to provide network support. Dave Walker pointed out that PCI interfaces are available for 10Base and 100Base Ethernet, 25Mbit/s to 155Mbit/s Asynchronous Transfer Mode (ATM), and even Fibre Distributed Data Interface (FDDI).

Phoebe has three Podule sockets, mounted on a riser card.
The full Podule Bus has been implemented to ensure hardware compatibility with existing devices.
A longer riser card, with more sockets, would be possible electrically. However, the case design limits further expansion this way.
The Podule Bus runs at 8MHz, as before.