EP2C8T144I8N Datasheet, PDF (382/470 Pages) Altera Corporation – Cyclone II Device Handbook, Volume 1

PS Configuration
You must connect all other configuration pins (nCONFIG, nSTATUS,
DCLK, DATA0, and CONF_DONE) to every Cyclone II device in the chain.
The configuration signals may require buffering to ensure signal integrity
and prevent clock skew problems. You should buffer the DCLK and DATA
lines for every fourth device. Because all device CONF_DONE pins are tied
together, all devices initialize and enter user mode at the same time.
Since all nSTATUS and CONF_DONE pins are connected, if any Cyclone II
device detects an error, configuration stops for the entire chain and the
entire chain must be reconfigured. For example, if the first Cyclone II
detects an error, it resets the chain by pulling its nSTATUS pin low. This
behavior is similar to a single Cyclone II device detecting an error.
If the Auto-restart configuration after error option is turned on, the
Cyclone II devices release their nSTATUS pins after a reset time-out
period (maximum of 40 µs). After all nSTATUS pins are released and
pulled high, the MAX II device reconfigures the chain without pulsing
nCONFIG low. If the Auto-restart configuration after error option is
turned off, the MAX II device must generate a low-to-high transition
(with a low pulse of at least 2 µs) on nCONFIG to restart the configuration
process.
If you want to delay the initialization of the devices in the chain, you can
use the CLKUSR pin option. The CLKUSR pin allows you to control when
your device enters user mode. This feature also allows you to control the
order of when each device enters user mode by feeding a separate clock
to each device’s CLKUSR pin. By using the CLKUSR pins, you can choose
any device in the multiple device chain to enter user mode first and have
the other devices enter user mode at a later time.
Different device families may require a different number of initialization
clock cycles. Therefore, if your multiple device chain consists of devices
from different families, the devices may enter user mode at a slightly
different time due to the different number of initialization clock cycles
required. However, if the number of initialization clock cycles is similar
across different device families or if the devices are from the same family,
then the devices enter user mode at the same time. See the respective
device family handbook for more information about the number of
initialization clock cycles required.
13–28
Cyclone II Device Handbook, Volume 1
Altera Corporation
February 2007