Interoperable 33 mhz and 66 mhz devices on the same pci bus

Abstract

An extended PCI bus (100) accepts both standard 33 MHz (101-102) and extended 66 MHz (103-104) PCI I/O devices, and permits the intermixing and interoperability of both types of devices on the same bus. Each extended 66 MHz initiator device (103) includes a target memory (205) that is programmed at boot up to include a list of address ranges of all extended 66 MHz devices. Each extended 66 MHz device includes a clock multiplier (202) that generates an internal 66 MHz clock signal by doubling the 33 MHz bus clock frequency. This clock multiplier may be in the form of a simple edge detecting frequency doubler (FIG. 4), or a phase locked loop (FIG. 5) that can also provide for phase adjustments to alter the skew between the bus and internal clocks. To transfer data between two extended 66 MHz devices, an extended initiator device sends, during the address/control phase of the bus cycle, a fast read or write command to the extended target device over the C/BE lines of the bus. Subsequently during the data phase of the bus cycle, data is transferred over the bus at the 66 MHz rate using the 66 MHz internal clock signals.