Chapter 9: Configuration, Design Security, and Remote System Upgrades in the Cyclone III Device Family
Configuration Features
9–37
In a multi-device PS configuration, the
nCE
pin of the first device is connected to
GND
while its
nCEO
pin is connected to the
nCE
pin of the next device in the chain. The
nCE
input of the last device comes from the previous device, while its
nCEO
pin is left
floating. After the first device completes configuration in a multi-device configuration
chain, its
nCEO
pin drives low to activate the
nCE
pin of the second device, which
prompts the second device to begin configuration. The second device in the chain
begins configuration in one clock cycle. Therefore, the transfer of data destinations is
transparent to the external host device. All other configuration pins (nCONFIG,
nSTATUS, DCLK, DATA[0],
and
CONF_DONE)
are connected to every device in the chain.
Configuration signals can require buffering to ensure signal integrity and prevent
clock skew problems. Ensure that the
DCLK
and
DATA
lines are buffered. Because all
device
CONF_DONE
pins are tied together, all devices initialize and enter user mode at
the same time.
If any device detects an error, configuration stops for the entire chain and the entire
chain must be reconfigured because all
nSTATUS
and
CONF_DONE
pins are tied together.
For example, if the first device flags an error on
nSTATUS,
it resets the chain by pulling
its
nSTATUS
pin low. This behavior is similar to a single device detecting an error.
You can have multiple devices that contain the same configuration data in your
system. To support this configuration scheme, all device
nCE
inputs are tied to GND,
while the
nCEO
pins are left floating. All other configuration pins (nCONFIG,
nSTATUS,
DCLK, DATA[0],
and
CONF_DONE)
are connected to every device in the chain.
Configuration signals can require buffering to ensure signal integrity and prevent
clock skew problems. Ensure that the
DCLK
and
DATA
lines are buffered. Devices must
be of the same density and package. All devices start and complete configuration at
the same time.
August 2012
Altera Corporation
Cyclone III Device Handbook
Volume 1
ALTERA [ ALTERA CORPORATION ]
