When connecting I
2
C Port 1 to multiple I/O expander ICs, the PEX 8632 has the option of having Hot Plug
capability on eight of its downstream Ports. The PEX 8632’s I
2
C Port 1 is the I
2
C Master, which is
designed to interface to I/O expander ICs, to build SHPCs. One 16-I/O expander connects to I
2
C Port 1
for a single SHPC, and one 40-I/O expander connects to I
2
C Port 1 for two SHPCs. 16- and 40-I/O
expander(s) cannot concurrently connect to the I
2
C Bus. To use 40-I/O expander(s), a register bit within
the PEX 8632 must be Set, and boot with serial EEPROM is essential. After the PEX 8632 is powered up,
the state machine inside the PEX 8632 scans the number of I/O expander ICs connecting to the I
2
C Bus,
starting from Address 000h, in ascending order. If the PEX 8632 cannot locate the device with
Address 000h, it stops the scan process. After the PEX 8632 locates the I/O expander IC, it automatically
assigns a valid Port Number for this SHPC.
illustrates a block diagram of the SHPC interface to
the PEX 8632. The SHPC has more signals than the PHPC. Besides the 10 Hot Plug signals mentioned
at the PHPC, INTERLOCK, SLOTID[3:0], and one GPIO are added to the SHPC. Also, the I/O expander's
Interrupt Output signal, INT#, should be connected to the PEX 8632’s Interrupt Input ball, SHPC_INT#,
for the PEX 8632 to service input events at the SHPC.
PEX 8632
SDA
SCL
INT#
16/40-I/O Expander
MAX7311 or
PCA9698
Interlock
Sltid[3:0]
GPIO
AD[2:0]
I
2
C
Port 1
PCI
Express
Slot
VCC
System
Power
Supply
12V, 3.3V
VCC
VCC
VCC
VCC
Hot Plug
Controller
FETs
Clock
Buffer
Clken#
Atnled#
Pwrled#
Pwren
Perst#
Button#
Pwrflt#
Mrl#
Prsnt#
Pwrgood
VCC
VCC
4
3
IO 13/29
IO 11/17
IO 0/16
IO 2/18
IO 3/19
IO 14/30
IO 4/20
IO 5/21
IO 6/22
IO[10:7]/[26:23]
IO 11/27
IO 12/28
IO 15/31
VCC
VCC
Figure 8. SHPC Interface to PEX 8632 Block Diagram
PEX 8632-AA Quick Start Hardware Design Guide, Version 1.1
10
© 2007 PLX Technology, Inc. All Rights Reserved.
