EP2S90F1020C5 Datasheet, PDF (613/768 Pages) Altera Corporation – Stratix II Device Handbook, Volume 1

Configuring Stratix II and Stratix II GX Devices
In multi-device PS configuration, the first device’s nCE pin is connected
to GND while its nCEO pin is connected to nCE of the next device in the
chain. The last device’s nCE input 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 second device’s nCE pin, prompting the second device to begin
configuration. All other configuration pins (nCONFIG, nSTATUS, DCLK,
DATA0, 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 for every fourth device.
When configuring multiple devices, configuration does not begin until all
devices release their OE or nSTATUS pins. Similarly, since 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 tied together, if any device
detects an error, configuration stops for the entire chain and the entire
chain must be reconfigured. For example, if the first device flags an error
on nSTATUS, it resets the chain by pulling its nSTATUS pin low. This low
signal drives the OE pin low on the enhanced configuration device and
drives nSTATUS low on all devices, causing them to enter a reset state.
This behavior is similar to a single device detecting an error.
If the Auto-restart configuration after error option is turned on, the
devices will automatically initiate reconfiguration if an error occurs. The
devices will release their nSTATUS pins after a reset time-out period
(maximum of 100 µs). When all the nSTATUS pins are released and pulled
high, the configuration device tries to reconfigure the chain. If the
Auto-restart configuration after error option is turned off, the external
system must monitor nSTATUS for errors and then pulse nCONFIG low
for at least 2 µs to restart configuration. The external system can pulse
nCONFIG if nCONFIG is under system control rather than tied to V_CC.
The enhanced configuration devices also support parallel configuration
of up to eight devices. The n-bit (n = 1, 2, 4, or 8) PS configuration mode
allows enhanced configuration devices to concurrently configure devices
or a chain of devices. In addition, these devices do not have to be the same
device family or density as they can be any combination of Altera devices.
An individual enhanced configuration device DATA line is available for
each targeted device. Each DATA line can also feed a daisy chain of
devices. Figure 7–23 shows how to concurrently configure multiple
devices using an enhanced configuration device.
Altera Corporation
January 2008
7–61
Stratix II Device Handbook, Volume 2