SGI Origin 2000 - Hardware Description - I/O Subsystem

I/O Subsystem

The I/O subsystem is based around the Crossbow (Xbow) ASIC, which shares many similarities with the SPIDER ASIC. Since the Xbow ASIC is intended for use with the simpler XIO protocol, its hardware is also simpler, allowing the ASIC to feature eight ports, compared with the SPIDER ASIC's six ports. Two of the ports connect to the node boards, and the remaining six to XIO cards. While the I/O subsystem's native bus is XIO, PCI-X and VME64 buses can also be used, provided by XIO bridges.

A IO6 base I/O board is present in every system. It is a XIO card that provides:

• 1 10/100BASE-TX port
• 2 Serial ports provided by dual UARTs
• 1 internal Fast 20 UltraSCSI single-ended port
• 1 external wide UltraSCSI, singled ended port
• 1 real-time interrupt output for frame sync
• 1 real-time interrupt input (edge triggered)
• Flash PROM, NVRAM and real time clock

The IO6G (G for Graphics) had 2 additional serial ports and keyboard/mouse ports plus the above ports. The IO6G was required on systems with the Onyx Graphics pipes(cards) to connect keyboard/mouse.