s5920 Applied Micro Circuits Corporation (AMCC), s5920 Datasheet - Page 145

• Manufacturer Part Number: s5920
• Description: Pci Product
• Manufacturer: Applied Micro Circuits Corporation (AMCC)

S5920 – PCI Product: Pass-Thru Operation
Figure 80. Active Mode PCI Read
Figure 20 shows a Pass-Thru write cycle with 0 wait
states for a 16-bit region. The PTBE[3:0]# signals are
used by the Add-On device to determine validity of the
current word cycle and also, which word of a long word
is currently being driven by the S5920. PTBE[3:0]#
encoding of Ch indicates the least significant 16-bit
portion of the 32-bit PCI data word is on the DQ[15:0]
bus. PTBE[3:0]# encoding of 3h indicates the most
significant 16-bit portion of the 32-bit PCI data word is
on the DQ[15:0] bus. PTADR# is shown as disabled in
Figure 20.
Figure 21 shows a Pass-Thru read cycle with 0 wait
states for a 16-bit region. PTADR# is disabled.
If the Add-On bus size is 8 bits, then the S5920 will
assert DXFR# 4 times for each 32-bit PCI word The
first completion is for byte 0, the second is for byte 1,
the third is for byte 3, and the fourth DXFR# assertion
is for byte 4 of a 32-bit word. If the current PCI access
has less than four bytes valid (PCI BE[3:0]# encoding
is not 0h), then the S5920 will still assert a 4-cycle
completion but one or more of them will not contain
valid data (PTBE[3:0]# = Fh).
As in Passive mode, in Active mode, the word read/
write order is determined by the Endian conversion
programmed into the S5920.
AMCC Confidential and Proprietary
PTATN#
PTBURST#
PTNUM[1:0]
PTWR
PTBE[3:0]
DXFR#
DQ[15:0]
PTWAIT#
PTADR#
ADCLK
1
2
Ch
LOW
1h
3
3h
HIGH
4
Fh
5
6
Figure 81. Active Mode PCI Write
Figure 22 shows a Pass-Thru write cycle with 0 wait
states for an 8-bit region. The PTBE[3:0]# signals are
used by the Add-On device to determine validity of the
current byte cycle and also, which byte of a long word
is currently being driven by the S5920. PTADR# is
enabled as an output.
CONFIGURATION
The S5920 Pass-Thru interface utilizes four Base
Address Registers (BADR1:4). Each Base Address
Register corresponds to a Pass-Thru region. The con-
tents of these registers during initialization determine
the characteristics of that particular Pass-Thru region.
Each region can be mapped to memory or I/O space.
Memory mapped devices can, optionally, be mapped
below 1 Mbyte and can be identified as prefetchable.
Both memory and I/O regions can be configured as 8,
16 or 32 bits wide.
Base Address Registers are loaded during initializa-
tion from the external non-volatile boot device. Without
an external boot device, the default value for the
BADR registers is zero (region disabled). The Base
Address Registers are the only registers that define
Pass-Thru operation. Consequently, the Pass-Thru
interface cannot be used without an external non-vola-
tile boot device.
PTATN#
PTBURST#
PTNUM[1:0]
PTWR
PTBE[3:0]
DXFR#
DQ[15:0]
PTWAIT#
PTADR#
ADCLK
1
2
Revision 1.02 – April 12, 2007
Ch
1h
LOW
3
3h
HIGH
4
Data Book
Fh
5
DS1596
6
145