IDT 89HPES24N3A, User Manual

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IDT SMBus Interfaces
PES24N3A User Manual 6 - 6 April 10, 2008
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), 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, 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 PES24N3A utilizes external SMBus/I2C-bus I/O expanders connected to the master SMBus inter-
face for hot-plug and port status signals. The PES24N3A is designed to work with Phillips PCA9555
compatible I/O expanders (i.e., PCA9555, PCA9535, and PCA9539). See the Phillips PCA9555 data sheet
for details on the operation of this device.
An external SMBus I/O expander provides 16 bit I/O pins that may be configured as inputs or outputs.
The PES24N3A supports up to five external I/O expanders. Table 6.4 summarizes the allocation of func-
tions to I/O expanders. I/O expanders zero through three are used to provide hot-plug I/O signals while I/O
expander four is used to provide link status and activity LED control.
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.
During the PES24N3A initialization, the SMBus/I2C-bus address allocated each I/O expander used in
that system configuration should be written to the corresponding IO Expander Address (IOE[0,2,4]ADDR)
field. The IOE[0,2]ADDR fields are contained in the I/O Expander Address 0 (IOEXPADDR0) register while
the IOE[4]ADDR field is contained in the SMBus I/O Expander Address 1 (IOEXPADDR1) register.
Hot-plug outputs and I/O expanders may be initialized via serial EEPROM. Since the I/O expanders and
serial EEPROM both utilize the master SMBus, no I/O expander transactions are initiated until serial
EEPROM initialization completes.
– Since no I/O expander transactions are initiated until serial EEPROM initialization completes, it is
not possible to toggle a hot-plug output through serial EEPROM initialization (i.e., it is not possible
to cause a 0
→
1
→
0 transition or a 1
→
0
→
1 transition).
Whenever the value of a IOExADDR field is modified, SMBus write transactions are issued to the corre-
sponding I/O expander by the PES24N3A to configure the device. This configuration initializes the direction
of each I/O expander signal and sets outputs to their default value. Outputs for ports that are disabled or are
not implemented in that configuration, are set to their negated value (e.g., the power indicator is turned off,
the link is down, there is no activity, etc.).
SMBus I/O
Expander
Section Function
0 Lower Port 2 hot-plug
Upper Port 4 hot-plug
2 Lower Reserved
Upper Power good inputs
4 Lower Link status
Upper Link activity
Table 6.4 I/O Expander Function Allocation