Configuring Cyclone II Devices
Cyclone II devices offer an optional INIT_DONEpin which signals the
end of initialization and the start of user mode with a low-to-high
transition. The Enable INIT_DONE output option is available in the
Quartus II software from the General tab of the Device & Pin Options
window. If you use the INIT_DONEpin, an external 10-kΩpull-up
resistor is required to pull the signal high when nCONFIGis low and
during the beginning of configuration. Once the optional bit to enable
INIT_DONEis programmed into the device (during the first frame of
configuration data), the INIT_DONEpin goes low. When initialization is
complete, the INIT_DONEpin is released and pulled high. This
low-to-high transition signals that the FPGA has entered user mode. If
you do not use the INIT_DONEpin, the initialization period is complete
after CONF_DONEgoes high and 299 clock cycles are sent to the CLKUSR
pin or after the time tCF2UM (see Table 13–8) if the Cyclone II device uses
the internal oscillator.
User Mode
When initialization is complete, the FPGA enters user mode. In user
mode, the user I/O pins no longer have weak pull-up resistors and
function as assigned in your design.
When the Cyclone II device is in user mode, you can initiate
reconfiguration by pulling the nCONFIGsignal low. The nCONFIGsignal
should be low for at least 2 µs. When nCONFIGis pulled low, the
Cyclone II device is reset and enters the reset stage. The Cyclone II device
also pulls nSTATUSand CONF_DONElow and all I/O pins are tri-stated.
Once nCONFIGreturns to a logic high level and nSTATUSis released by
the Cyclone II device, reconfiguration begins.
Error During Configuration
If an error occurs during configuration, the Cyclone II device drives the
nSTATUSsignal low to indicate a data frame error, and the CONF_DONE
signal stays low. If you enable the Auto-restart configuration after error
option in the Quartus II software from the General tab of the Device &
Pin Options dialog box, the Cyclone II device resets the serial
configuration device by pulsing nCSO, releases nSTATUSafter a reset
time-out period (about 40 µs), and retries configuration. If the
Auto-restart configuration after error option is turned off, the external
system must monitor nSTATUSfor errors and then pull nCONFIGlow for
at least 2 µs to restart configuration.
1
If you use the optional CLKUSRpin and the nCONFIGpin is
pulled low to restart configuration during device initialization,
ensure CLKUSRcontinues to toggle during the time nSTATUSis
low (a maximum of 40 μs).
Altera Corporation
February 2007
13–11
Cyclone II Device Handbook, Volume 1
ALTERA [ ALTERA CORPORATION ]
