C.1.2 PCI Bus

The peripheral component interconnect (PCI) bus is a high-performance 32-bit or 64-bit bus with multiplexed address and data lines. The PCI bus provides electrical interconnection between highly integrated peripheral controller components, peripheral add-on devices, and the processor/memory system.

There are two PCI buses. The first bus is a one-slot, 3.3-VDC, 64-bit or 32-bit, 66-MHz or 33-MHz bus. The second bus is a three-slot, 5.0-VDC, 64-bit or 32-bit, 33-MHz bus. Each bus is controlled by the UPA-to-PCI bridge (U2P) ASIC. There are also two on-board controllers, the Symbios 53C876 SCSI controller and the PCI-to-Ebus/Ethernet controller (PCIO) ASIC, on the 33-MHz PCI bus.

C.1.2.1 U2P ASIC

The UPT-to-PCI bridge (U2P) ASIC controls the PCI buses. It forms the bridge from the UPA bus to the PCI buses. For a brief description of the U2P ASIC, see "C.1.12 ASICs".

C.1.2.2 Symbios 53C876 SCSI Controller

The Symbios 53C876 SCSI controller provides electrical connection between the main logic board and the internal and external SCSI buses to the PCI bus. The Symbios controller is two SCSI controllers on the same PCI slot. Controller "A" is used to interface to internal devices. The second controller, controller "B," is used to interface to external devices.

C.1.2.3 PCIO ASIC

The PCI-to-EBus/Ethernet controller (PCIO) ASIC bridges the PCI bus to the EBus, enabling communication between the PCI bus and all miscellaneous I/O functions, as well as the connection to slower on-board functions. The PCIO ASIC also embeds the Ethernet controller.