Hi Sundar-
Indeed, my experience shows the interface between keypad readers and EAC panels is indeed mostly Wiegand.
For specific details on the format of data transferred over the Wiegand interface when a PIN is entered, I recommend you download the reference document obtained by following this link: http://www.farpointedata.com/datasheets/qsg_and_ref/KeypadMode_REF.pdf.
A couple of extraneous points:
4-bit word style: common with many HID readers;
8-bit word style: widely supported and follows the legacy Dorodo PIN output;
26-bit Wiegand: a catch all for situations where the 4-bit or 8-bit word styles are not supported. Limitation is PIN length (five characters/digits), as this is typically represented by the 16-bit ID field.
Hope this is what you are looking for. If you still have questions, please feel free to give me a call.
Best,
Scott