8–8
Chapter 8: Using MAX II Devices in Multi-Voltage Systems
Hot Socketing
For signals with duty cycle greater than 30% on MAX II input pins, Altera
recommends a VCCIO voltage of 3.0 V to guarantee long-term I/O reliability. For signals
with duty cycle less than 30%, the VCCIO voltage can be 3.3 V.
Hot Socketing
For information about hot socketing, refer to the Hot Socketing and Power-On Reset in
MAX II Devices chapter in the MAX II Device Handbook.
Power-Up Sequencing
MAX II devices are designed to operate in multiple-voltage environments where it
may be difficult to control power sequencing. Therefore, MAX II devices are designed
to tolerate any possible power-up sequence. Either VCCINT or VCCIO can initially supply
power to the device, and 3.3-V, 2.5-V, 1.8-V, or 1.5-V input signals can drive the
devices without special precautions before VCCINT or VCCIO is applied. MAX II devices
can operate with a VCCIO voltage level that is higher than the VCCINT level.
When VCCIO and VCCINT are supplied from different power sources to a MAX II device, a
delay between VCCIO and VCCINT may occur. Normal operation does not occur until both
power supplies are in their recommended operating range. When VCCINT is powered-
up, the IEEE Std. 1149.1 Joint Test Action Group (JTAG) circuitry is active. If the TMS
and TCKare connected to VCCIO and VCCIO is not powered-up, the JTAG signals are left
floating. Thus, any transition on TCKcan cause the state machine to transition to an
unknown JTAG state, leading to incorrect operation when VCCIO is finally powered-up.
To disable the JTAG state during the power-up sequence, TCKshould be pulled low to
ensure that an inadvertent rising edge does not occur on TCK.
Power-On Reset
For information about Power-On Reset (POR), refer to the Hot Socketing and Power-On
Reset in MAX II Devices chapter in the MAX II Device Handbook.
Conclusion
MAX II devices have MultiVolt I/O support, allowing 1.5-V, 1.8-V, 2.5-V, and 3.3-V
devices to interface directly with MAX II devices without causing voltage conflicts. In
addition, MAX II devices can interface with 5.0-V devices by slightly modifying the
external hardware interface and enabling I/O clamp diodes via the Quartus II
software. This MultiVolt capability also enables the device core to run at its core
voltage, VCCINT, while maintaining I/O pin compatibility with other devices. Altera has
taken further steps to make system design easier by designing devices that allow
V
CCINT and VCCIO to power-up in any sequence and by incorporating support for hot
socketing.
MAX II Device Handbook
© October 2008 Altera Corporation
ALTERA [ ALTERA CORPORATION ]
