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IDT SMBus Interfaces
Notes
PES4T4 User Manual
Writing a one to the Reload I/O Expander Signals (RELOADIOEX) bit in the IOEXPINTF register causes
the PES4T4 to generate SMBus write and read transactions to the I/O expander number selected in the
SEL field. This results in the value of the IOEDATA field being updated to reflect the current state of the
corresponding I/O expander signals. This feature may be used to aid in debugging I/O expander operation.
For example, a user who neglects to configure a GPIO as an alternate function may use this feature to
determine that master SMBus transactions to the I/O expander function properly and that the issue is with
the interrupt logic.
The IO Expander Test Mode (IOEXTM) bit in the IOEXPTINF register allows an I/O expander test mode
to be entered. When this bit is set, the PES4T4 core logic outputs are ignored and the values written to the
I/O expander for output bits are the values in the IOEDATA field. In this mode, the PES4T4 issues a trans-
action to update the state of the I/O expander whenever a bit corresponding to an I/O expander output
changes state due to a write to the IOEDATA field. Bits in the IOEDATA field that correspond to outputs are
dependent on the I/O expander number selected in the SEL field in the IOEXPINTF register. The outputs for
each I/O expander number are shown in Table 6.5 through 6.8.
System design recommendations:
– I/O expander addresses and default output values may be configured during serial EEPROM
initialization. If I/O expander addresses are configured via the serial EEPROM, the PES4T4 will
initialize the I/O expanders when normal device operation begins following the completion of the
fundamental reset sequence.
– If the I/O expanders are initialized via serial EEPROM, the data value for output signals during the
SMBus initialization sequence will correspond to those at the time the SMBus transactions are
initiated. It is not possible to toggle SMBus I/O expander outputs by modifying data values during
serial EEPROM initialization.
– During a fundamental reset and before the I/O expander outputs are initialized, all I/O expander
output signals default to inputs. Therefore, pull-up or pull-down resistors should be placed on
outputs to ensure that they are held in the desired state during this period.
– All hot-plug data value modifications that correspond to hot-plug outputs result in SMBus transac-
tions. This includes modifications due to upstream secondary bus resets and hot-resets.
– I/O expander outputs are not modified when the device transitions from normal operation to a
fundamental reset. In systems where I/O expander output values must be reset during a funda-
mental reset, a PCA9539 I/O expander should be used.
I/O Expander 0
SMBus I/O
Expander
Type
Bit
1
0 (I/O-0.0)
I
1 (I/O-0.1)
I
2 (I/O-0.2)
I
3 (I/O-0.3)
I
4 (I/O-0.4)
O
5 (I/O-0.5)
O
6 (I/O-0.6)
O
7 (I/O-0.7)
O
8 (I/O-1.0)
I
9 (I/O-1.1)
I
Signal
P2APN
Port 2 attention push button input
P2PDN
Port 2 presence detect input
P2PFN
Port 2 power fault input
P2MRLN
Port 2 manually-operated retention latch (MRL)
input
P2AIN
Port 2 attention indicator output
P2PIN
Port 2 power indicator output
P2PEP
Port 2 power enable output
P2ILOCKP
Port 2 electromechanical interlock
P4APN
Port 4 attention push button input
P4PDN
Port 4 presence detect input
Table 6.5 I/O Expander 0 Signals (Part 1 of 2)
6 - 8
Description
February 1, 2011
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