The Spartan-3E Tutorial 2 : Introduction to using the PicoBlaze Microcontroller Version 1.0
http://eprints.qut.edu.au/55385/1/Spartan3E_Tutorial_2.pdf

PicoBlaze 8-bit Embedded Microcontroller User Guid
http://www.xilinx.com/support/documentation/ip_documentation/ug129.pdf