Intel 21555 - Manual (Page 30)

30 21555 Non-Transparent PCI-to-PCI Bridge User Manual
Signal Descriptions
3.4 Secondary PCI Bus Interface 64
-
Bit Extension
Signals
Table 9 describes the secondary PCI bus interface 64-bit extension signals. The letters in the “Type” column are
described in Table 1 .
Table 9. Secondary PCI Bus Interface 64 - Bit Extension Signals (Sheet 1 of 2)
Signal Name Type Description
s_ack64_l STS
Secondary PCI interface acknowledge 64-bit transfer.
Signal s_ack64_l should never be driven when s_req64_l is not driven.
Signal s_ack64_l is asserted by the target only when s_req64_l is asserted by the
initiator, to indicate the target’s ability to transfer data using 64 bits.
Signal s_ack64_l has the same timing as s_devsel_l. When deasserting,
s_ack64_l is driven to a deasserted state for one clock cycle and is then sustained
by an external pull-up resistor.
s_ad[63:32] TS
Secondary PCI interface address and data upper 32 bits.
The 21555 does not bus park these pins. These pins are tristated during the
assertion of s_rst_l. Signals s_ad[63:32] are driven to a valid value when the 64-bit
extension is disabled (s_req64_l is deasserted during s_rst_l assertion).
This multiplexed address and data bus provides an additional 32 bits to the
secondary interface. During the address phase or phases of a transaction, when the
dual-address command is used and s_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 s_req64_l and s_ack64_l are
both asserted.
When not driven, signals s_ad[63:32] are pulled up to a valid logic level through
external resistors.
s_cbe_l[7:4] TS
Secondary 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 s_rst_l. Signals s_cbe_l[7:4] are driven to a valid value when the
64-bit extension is disabled (s_req64_l is deasserted during s_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 s_req64_l is asserted, the initiator drives the transaction type on s_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 s_ad[63:32] data bits on s_cbe_l[7:4] during the data phases, when s_req64_l
and s_ack64_l are both asserted.
When not driven, signals s_cbe_l[7:4] are pulled up to a valid logic level through
external resistors.