EP2S90F1020C5 Datasheet, PDF (631/768 Pages) Altera Corporation – Stratix II Device Handbook, Volume 1

Configuring Stratix II and Stratix II GX Devices
configuration chain, the second device’s RDYnBSY pin will be high during
the time that the first device is being configured. When the first device has
been successfully configured, it will drive nCEO low to activate the next
device in the chain and drive its RDYnBSY pin high. Therefore, since
RDYnBSY signal is driven high before configuration and after
configuration before entering user-mode, the device being configured
will govern the output of the AND gate.
The nRS signal can be used in multi-device PPA chain because the
Stratix II and Stratix II GX devices tri-state the DATA[7..0] pins before
configuration and after configuration before entering user-mode to avoid
contention. Therefore, only the device that is currently being configured
responds to the nRS strobe by asserting DATA7.
All other configuration pins (nCONFIG, nSTATUS, DATA[7..0], nCS,
CS, nWS, nRS and CONF_DONE) are connected to every device in the chain.
It is not necessary to tie nCS and CS together for every device in the chain,
as each device’s nCS and CS input can be driven by a separate source.
Configuration signals may require buffering to ensure signal integrity
and prevent clock skew problems. Ensure that the DATA lines are buffered
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 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
behavior is similar to a single device detecting an error.
If the Auto-restart configuration after error option is turned on, the
devices release their nSTATUS pins after a reset time-out period
(maximum of 100 µs). After all nSTATUS pins are released and pulled
high, the microprocessor can try to reconfigure the chain without needing
to pulse nCONFIG low. If this option is turned off, the microprocessor
must generate a low-to-high transition (with a low pulse of at least 2 µs)
on nCONFIG to restart the configuration process.
In your system, you may have multiple devices that contain the same
configuration data. To support this configuration scheme, all device nCE
inputs are tied to GND, while nCEO pins are left floating. All other
configuration pins (nCONFIG, nSTATUS, DATA[7..0], nCS, CS, nWS,
nRS and CONF_DONE) are connected to every device in the chain.
Configuration signals may require buffering to ensure signal integrity
and prevent clock skew problems. Ensure that the DATA lines are buffered
for every fourth device. Devices must be the same density and package.
Altera Corporation
January 2008
7–79
Stratix II Device Handbook, Volume 2