说明：  控制SRAM的读写； 向SRAM中写入12个数据，这12个数据由助教随机给出； 当按下4×3键盘上的按键时，读出对应的数据，并显示在七段数码管上； SRAM为16位，用16进制表示为4位字符，对应4个七段数码管；
(Control SRAM read and write write to the SRAM 12 data, the 12 random data is given by the TA when you press the 4 × 3 keys on the keyboard when the corresponding data read and displayed in the seven-segment LED on SRAM is 16 bits, that is 4 by 16 hexadecimal characters, corresponding to four seven-segment LED )