21150

The 21150 is a second-generation PCI-to-PCI bridge and is fully compliant with PCI Local Bus Specification, Revision 2.1. The 21150 provides full support for delayed transactions, which enables the buffering of memory read, I/O, and configuration transactions. The 21150 has separate posted write, read data, and delayed transaction queues with significantly more buffering capability than first-generation bridges. In addition, the 21150 supports buffering of simultaneous multiple posted write and delayed transactions in both directions. Among the features provided by the 21150 are a programmable 2-level secondary bus arbiter, an IEEE standard 1149.1 JTAG interface, live insertion support, a 4-pin general-purpose I/O interface, individual secondary clock disables, and enhanced address decoding. The 21150 has sufficient clock and arbitration pins to support nine PCI bus master devices directly on its secondary interface.

The 21150 allows the two PCI buses to operate concurrently. This means that a master and a target on the same PCI bus can communicate while the other PCI bus is busy. This traffic isolation may increase system performance in applications such as multimedia.

The 21150 makes it possible to extend a system's load capability limit beyond that of a single PCI bus by allowing motherboard designers to add more PCI devices or more PCI option card slots than a single PCI bus can support. Figure 1 illustrates the use of two 21150 PCI-to-PCI bridges on a system board. Each 21150 that is added to the board creates a new PCI bus that provides support for the additional PCI slots or devices

Option card designers can use the 21150 to implement multiple-device PCI option cards. Without a PCI-to-PCI bridge, PCI loading rules would limit option cards to one device. The PCI Local Bus Specification) loading rules limit PCI option cards to a single connection per PCI signal in the option card connector. The 21150 overcomes this restriction by providing, on the option card, an independent PCI bus to which up to nine devices can be attached. Figure 2 shows how the 21150 enables the design of a multicomponent option card.