Hi,
Thank you for contacting Intel community.
Please be noted that EP3SE50F484C2 has been obsolete hence we have limited information for the device. However it is recommended to refer to Stratix III handbook(page 349) for further information on Fast Active Serial and EPCS datasheet for EPCS.
Stratix III handbook:
https://www.intel.com/content/dam/www/programmable/us/en/pdfs/literature/hb/stx3/stratix3_handbook.pdf
EPCS datasheet:
https://www.intel.com/content/dam/www/programmable/us/en/pdfs/literature/hb/cfg/cyc_c51014.pdf
Thank you.
Regards,
Aiman