单片CPU接口设计
端口定义：
mbeb：接口类型定义，1为intel模式，0为moto模式
wr_rwb:intel模式下，低电平为写有效；moto模式下，低电平为写有效，高电平为读有效；
rd_eb：intel模式下，低电平为读有效；moto模式下，高电平为读允许；
a：地址输入，（5:0）
d：双向数据总线，（7:0）
rd：低电平内部电路读有效
wr：低电平内部电路写有效
add：内部电路读写地址
mbd_in:cpu写入内部寄存器的数据（7:0）
mbd_out:内部电路寄存器读出的值，送往CPU (7:0)(Design of single chip CPU interface
Port definition:
Mbeb: interface type definition, 1 for Intel mode, 0 for moto mode
In the wr_rwb:intel mode, the low level is valid for writing; in the moto mode, the low level is valid for write, and the high level is effective for reading.
In the rd_eb:intel mode, the low level is valid for reading; in the moto mode, the high level is read allow.
A: address input, (5:0)
D: bi-directional data bus, (7:0)
Rd: low level internal circuit read effective
WR: low level internal circuit write effectiveness
Add: the read and write address of the internal circuit
Mbd_in:cpu writes the data in the internal register (7:0)
Mbd_out: internal circuit register readout values, sent to CPU (7:0))