
IDT SMBus Interfaces
PES32NT24xG2 User Manual
12 - 11
January 30, 2013
Notes
To write a byte to the serial EEPROM, the root should configure the ADDR field with the byte address of
the serial EEPROM location to be written and set the OP field to “write.” If the serial EEPROM is not busy
(i.e., the BUSY bit is cleared), then the write operation may be initiated by writing the value to be written to
the DATA field. When the write operation completes, the DONE bit is set and the busy bit is cleared.
Initiating a serial EEPROM read or write operation when the BUSY bit is set produces undefined results.
SMBus errors may occur when accessing the serial EEPROM. If an error occurs, then it is reported in
the SMBus Status (SMBUSSTS) register. Software should check for errors before and after each serial
EEPROM access.
I/O Expanders
The PES32NT24xG2 utilizes external SMBus/I
2
C-bus I/O Expanders connected to the master SMBus
interface for hot-plug and port status signals. The switch is designed to work with Phillips PCA9555 compat-
ible I/O Expanders (i.e., PCA9555, PCA9535, and PCA9539). See the Phillips PCA9555 data sheet for
details on the operation of this device.
Note: The MAX7311 is recommended since it is Phillips PCA9555-compatible and supports 64 slave
addresses. This allows the use of many I/O Expanders on the same SMBus.
An external SMBus I/O Expander provides 16 bit I/O pins that may be configured as inputs or outputs.
The PES32NT24xG2 supports up to 22 external I/O expanders. Table 12.4 summarizes the allocation of
functions to I/O expanders. I/O expander signals associated with LED control (i.e., link status and activity)
are active low (i.e., driven low when an LED should be turned on). I/O expander signals associated with hot-
plug signals are not inverted.
SMBus I/O
Expander
Section
Functionality
0
Lower
Port 0 hot-plug
Upper
Port 4 hot-plug
1
Lower
Port 8 hot-plug
Upper
Port 16 hot-plug
2
Lower
Port 2 hot-plug
Upper
Port 6 hot-plug
3
Lower
Port 12 hot-plug
Upper
Port 20 hot-plug
4
Lower
Port 1 hot-plug
Upper
Port 3 hot-plug
5
Lower
Port 5 hot-plug
Upper
Port 7 hot-plug
6
Lower
Port 10 hot-plug
Upper
Port 14 hot-plug
7
Lower
Port 18 hot-plug
Upper
Port 22 hot-plug
8
Lower
Port 9 hot-plug
Upper
Port 11 hot-plug
Table 12.4 I/O Expander Functionality Allocation (Part 1 of 2)
Содержание PCI Express 89HPES32NT24xG2
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Страница 28: ...IDT List of Figures PES32NT24xG2 User Manual xviii January 30 2013 Notes...
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