9–10
Chapter 9: Configuration, Design Security, and Remote System Upgrades in the Cyclone III Device Family
Configuration Features
Initialization
In Cyclone III device family, the clock source for initialization is either a 10-MHz
(typical) internal oscillator (separate from the AS internal oscillator) or an optional
CLKUSRpin. By default, the internal oscillator is the clock source for initialization. If
you use the internal oscillator, the device provides itself with enough clock cycles for a
proper initialization. When using the internal oscillator, you do not need to send
additional clock cycles from an external source to the CLKUSRpin during the
initialization stage. Additionally, you can use the CLKUSRpin as a user I/O pin.
You also have the flexibility to synchronize initialization of multiple devices or to
delay initialization with the CLKUSR option. The CLKUSRpin allows you to control
when your device enters user mode for an indefinite amount of time. You can turn on
the Enable user-supplied start-up clock (CLKUSR) option in the Quartus II software
from the General tab of the Device and Pin Options dialog box. When you turn on
the Enable user supplied start-up clock option (CLKUSR) option, the CLKUSRpin is
the initialization clock source. Supplying a clock on the CLKUSRpin does not affect the
configuration process. After the configuration data is accepted and CONF_DONEgoes
high, the Cyclone III device family requires a certain amount of clock cycles to
initialize and to enter user mode.
Table 9–5 lists the required clock cycles for proper initialization in Cyclone III device
family.
Table 9–5. Initialization Clock Cycles Required in Cyclone III Device Family
Device
Initialization Clock Cycles
Cyclone III
3,185
3,192
Cyclone III LS
Table 9–6 lists the maximum CLKUSR frequency (fMAX) for Cyclone III device family.
Table 9–6. Maximum CLKUSR Frequency for Cyclone III Device Family
Device
fMAX (MHz)
133
Cyclone III
Cyclone III LS
100
1
If you use the optional CLKUSRpin and the nCONFIGpin is pulled low to restart
configuration during device initialization, ensure that the CLKUSRpin continues to
toggle when nSTATUSis low (a maximum of 230 s).
User Mode
An optional INIT_DONEpin is available that 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 and
Pin Options dialog box. If you use the INIT_DONEpin, it is high due to an external
10-k pull-up resistor when nCONFIGis low and during the beginning of
configuration. After the option bit to enable INIT_DONEis programmed into the device
Cyclone III Device Handbook
Volume 1
August 2012 Altera Corporation
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