Chapter 9: Configuration, Design Security, and Remote System Upgrades in the Cyclone III Device Family
9–9
Configuration Features
When the device exits POR, all user I/O pins continue to tri-state. The user I/O pins
and dual-purpose I/O pins have weak pull-up resistors that are always enabled (after
POR) before and during configuration. After POR, the Cyclone III device family
releases nSTATUS, which is pulled high by an external 10-k pull-up resistor and
enters configuration mode.
When nCONFIGgoes high, the device exits reset and releases the open-drain nSTATUS
pin, which is then pulled high by an external 10-kpull-up resistor. After nSTATUSis
released, the device is ready to receive configuration data and the configuration stage
begins.
Cyclone III LS devices are accessible by limited JTAG instructions after POR. For more
information about enabling full JTAG instructions access, refer to “JTAG Instructions”
on page 9–60.
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For more information about the value of weak pull-up resistors on the I/O pins that
are on before and during configuration, refer to the Cyclone III Device Data Sheet and
Cyclone III LS Device Data Sheet chapters.
Configuration
Configuration data is latched into the Cyclone III device family at each DCLKcycle.
However, the width of the data bus and the configuration time taken for each scheme
are different. After the device receives all the configuration data, the device releases
the open-drain CONF_DONEpin, which is pulled high by an external 10-kpull-up
resistor. A low-to-high transition on the CONF_DONEpin indicates that configuration is
complete and initialization of the device can begin. The CONF_DONEpin must have an
external 10-k pull-up resistor for the device to initialize.
You can begin reconfiguration by pulling the nCONFIGpin low. The nCONFIGpin must
be low for at least 500 ns. When nCONFIGis pulled low, the Cyclone III device family is
reset. The Cyclone III device family also pulls nSTATUSand CONF_DONElow and all I/O
pins are tri-stated. When nCONFIGreturns to a logic-high level and nSTATUSis released
by the Cyclone III device family, reconfiguration begins.
Configuration Error
If an error occurs during configuration, the Cyclone III device family asserts the
nSTATUSsignal low, indicating a data frame error, and the CONF_DONEsignal stays low.
If the Auto-restart configuration after error option (available in the Quartus II
software from the General tab of the Device and Pin Options dialog box) is turned
on, the Cyclone III device family releases nSTATUSafter a reset time-out period (a
maximum of 230 s), and retries configuration. If this option is turned off, the system
must monitor nSTATUSfor errors and then pulse nCONFIGlow for at least 500 ns to
restart configuration.
August 2012 Altera Corporation
Cyclone III Device Handbook
Volume 1
ALTERA [ ALTERA CORPORATION ]
