PI7C8140AMAE Pericom Semiconductor, PI7C8140AMAE Datasheet - Page 34

• Manufacturer Part Number: PI7C8140AMAE
• Description: IC PCI-PCI BRIDGE 2PORT 128-QFP
• Manufacturer: Pericom Semiconductor

Specifications of PI7C8140AMAE

• Applications: *
• Interface: *
• Voltage - Supply: *
• Package / Case: 128-QFP
• Mounting Type: Surface Mount
• Maximum Operating Temperature: + 85 C
• Minimum Operating Temperature: 0 C
• Mounting Style: SMD/SMT
• Operating Supply Voltage: 3 V to 3.6 V
• Supply Current (max): 230 mA
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

07-0067
3.2.1 I/O BASE AND LIMIT ADDRESS REGISTER
3.2.2 ISA MODE
the bridge response to the secondary bus I/O transactions is not predictable. Configure the I/O base
and limit address registers, ISA enable bit, VGA mode bit, and VGA snoop bit before setting I/O enable
and master enable bits, and change them subsequently only when the primary and secondary PCI buses
are idle.
The bridge implements one set of I/O base and limit address registers in configuration space that define
an I/O address range per port downstream forwarding. The bridge supports 32-bit I/O addressing, which
allows I/O addresses downstream of the bridge to be mapped anywhere in a 4GB I/O address space.
I/O transactions with addresses that fall inside the range defined by the I/O base and limit registers are
forwarded downstream from the primary PCI bus to the secondary PCI bus. I/O transactions with
addresses that fall outside this range are forwarded upstream from the secondary PCI bus to the primary
PCI bus.
The I/O range can be turned off by setting the I/O base address to a value greater than that of the I/O
limit address. When the I/O range is turned off, all I/O trans-actions are forwarded upstream, and no I/O
transactions are forwarded downstream. The I/O range has a minimum granularity of 4KB and is
aligned on a 4KB boundary. The maximum I/O range is 4GB in size. The I/O base register consists of
an 8-bit field at configuration address 1Ch, and a 16-bit field at address 30h. The top 4 bits of the 8-bit
field define bits [15:12] of the I/O base address. The bottom 4 bits read only as 1h to indicate that the
bridge supports 32-bit I/O addressing. Bits [11:0] of the base address are assumed to be 0, which
naturally aligns the base address to a 4KB boundary. The 16 bits contained in the I/O base upper 16 bits
register at configuration offset 30h define AD[31:16] of the I/O base address. All 16 bits are read/write.
After primary bus reset or chip reset, the value of the I/O base address is initialized to 0000 0000h.
The I/O limit register consists of an 8-bit field at configuration offset 1Dh and a 16-bit field at offset
32h. The top 4 bits of the 8-bit field define bits [15:12] of the I/O limit address. The bottom 4 bits read
only as 1h to indicate that 32-bit I/O addressing is supported. Bits [11:0] of the limit address are
assumed to be FFFh, which naturally aligns the limit address to the top of a 4KB I/O address block. The
16 bits contained in the I/O limit upper 16 bits register at configuration offset 32h define AD[31:16] of
the I/O limit address. All 16 bits are read/write. After primary bus reset or chip reset, the value of the
I/O limit address is reset to 0000 0FFFh.
Note: The initial states of the I/O base and I/O limit address registers define an I/O range of 0000 0000h
to 0000 0FFFh, which is the bottom 4KB of I/O space. Write these registers with their appropriate
values before setting either the I/O enable bit or the master enable bit in the command register in
configuration space.
The bridge supports ISA mode by providing an ISA enable bit in the bridge control register in
configuration space. ISA mode modifies the response of the bridge inside the I/O address range in order
to support mapping of I/O space in the presence of an ISA bus in the system. This bit only affects the
response of the bridge when the transaction falls inside the address range defined by the I/O base and
limit address registers, and only when this address also falls inside the first 64KB of I/O space (address
bits [31:16] are 0000h). When the ISA enable bit is set, the bridge does not forward downstream any
I/O transactions addressing the top 768 bytes of each aligned 1KB block. Only those transactions
addressing the bottom 256 bytes of an aligned 1KB block inside the base and limit I/O address range
Page 34 of 82
2-PORT PCI-TO-PCI BRIDGE
March 20, 2007 – Revision 1.01
PI7C8140A