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26 21555 Non-Transparent PCI-to-PCI Bridge User Manual
Signal Descriptions
3.2 Primary PCI Bus Interface 64-Bit Extension Signals
Table 7 describes the primary PCI bus interface 64-bit extension signals. The letters in the “Type” column are
described in Table 1.
Table 7. Primary PCI Bus Interface 64
-Bit Extension Signals (Sheet 1 of 2)
Signal Name Type Description
p_ack64_l STS
Primary PCI interface acknowledge 64-bit transfer.
Signal p_ack64_l should never be driven when p_req64_l is not driven.
Signal p_ack64_l is asserted by the target only when p_req64_l is asserted by the
initiator, to indicate the target’s ability to transfer data using 64 bits.
Signal p_ack64_l has the same timing as p_devsel_l.
When deasserting, p_ack64_l is driven to a deasserted state for one clock cycle
and is then sustained by an external pull-up resistor.
p_ad[63:32] TS
Primary PCI interface address and data upper 32 bits.
The 21555 does not bus park these pins. These pins are tristated during the
assertion of p_rst_l. Signals p_ad[63:32] are driven to a valid value when the 64-bit
extension is disabled (p_req64_l is deasserted during p_rst_l assertion).
This multiplexed address and data bus provides an additional 32 bits to the primary
interface. During the address phase or phases of a transaction, when the
dual-address command is used and p_req64_l is asserted, the initiator drives the
upper 32 bits of a 64-bit address; otherwise, these bits are undefined, and the
initiator drives a valid logic level onto the pins.
During the data phases of a transaction, the initiator drives the upper 32 bits of
64-bit write data, or the target drives the upper 32 bits of 64-bit read data, when
p_req64_l and p_ack64_l are both asserted.
When not driven, signals p_ad[63:32] are pulled up to a valid logic level through
external resistors.
p_cbe_l[7:4] TS
Primary PCI interface command and byte enables upper 4 bits.
The 21555 does not bus park these pins. These pins are tristated during the
assertion of p_rst_l. Signals p_cbe_l[7:4] are driven to a valid value when the
64-bit extension is disabled (p_req64_l is deasserted during p_rst_l assertion).
These signals are a multiplexed command field and byte enable field. During the
address phase or phases of a transaction, when the dual-address command is used
and p_req64_l is asserted, the initiator drives the transaction type on p_cbe_l[7:4];
otherwise, these bits are undefined, and the initiator drives a valid logic level onto
the pins.
For both read and write transactions, the initiator drives byte enables for the
p_ad[63:32] data bits on p_cbe_l[7:4] during the data phases, when p_req64_l
and p_ack64_l are both asserted.
When not driven, signals p_cbe_l[7:4] are pulled up to a valid logic level through
external resistors.