这是一段vhdl程序，它是由桂林电子科大编写，完成stack功能-vhdl This is a process, which is prepared from Guilin UESTC complete stack functions

Prawn is a simple eight-bit microprocessor based on the sample processor described in Chapter 9 of "VHDL : Analysis and Modeling of Digital Systems"by Z. Navabi, McGraw-Hill,Inc. 1993. We have added some features such as interrupt, stack and some con