Re: quetions about configure altera fpga(apex20k) using ppa scheme

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Hello,
When using passive parallel asynchronous (PPA) mode, the APEX device
has a built-in oscillator that controls its response to the nWS and
other signals. There is some variation of this oscillator's speed
depending on temperature, voltage, and process.

When you drive nWS low then high, the device captures the byte of data
on the DATA[7..0] bus and then starts to process it, clocked by the
internal oscillator. During this time it will drive the RDYnBSY line
low. When it drives the RDYnBSY line high, it has completed.

When you drive in the final byte of data, the device will drive
RDYnBSY low then high. CONF_DONE will not be released until after it
has driven RDYnBSY high again. On an APEX 20KE device, tBUSY (the time
during which RDYnBSY is low) ranges from 0.4 to 1.6 microseconds.

Note that the configuration files that Quartus II software generates
include some number of 1s at the end of the file. The reason for doing
so is that with other configuration modes (such as passive serial),
the system must clock the device after CONF_DONE goes high to get it
into user mode. Quartus II adds the extra bits so that a user can just
drive in the whole file and by doing so clock the device enough times
to initialize it - the user does not have to drive in the data and
then separately clock it. A small thing but it makes it easier to use.
When using PPA, this means that CONF_DONE will go high before you have
sent in the entire file. If you have chosen the internal oscillator as
the clock source for initializing the device, the device may even
enter user mode before you have sent in the entire file. (This choice
is one of the device options, chosen when you select the configuration
mode).

Finally, note that depending on your use of the dual-purpose pins,
there may be no harm in sending in the entire configuration file, and
doing so can make the system design a little easier. For example, the
data bus pins DATA[7..1] are used for configuration in PPA mode, but
may take on a different functionality in user mode. If those pins are
programmed to be inputs in user mode, then continuing to drive in the
extra 1s at the end of the configuration file will be ok. But if they
are programmed to be outputs, then you could have contention.

So the short answer to your question is that CONF_DONE will go high
after RDYnBSY goes low then high again. The long answer is that
depending on the overall setup, sending the extra bytes may not
matter.

Sincerely,
Greg Steinke
snipped-for-privacy@altera.com
Altera Corporation





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