半加器和全加器逻辑？

Question

我无法通过半加器和全加器测试，我想知道我在 FullAdder() 和 HalfAdder() 方法中的逻辑有什么问题？ None 我的测试似乎由于某种原因通过了...

代码如下：

    # All wires that enter/exit the circuit need to be visible outside of the 
    # function: they are to be created in the enclosing scope and passed 
    # as parameters.
    # However, wires that connect the AND gates to the OR gates are 
    # _internal wires_, visible only inside the circuit: they need to be created
    xy = self.Wire('xy')
    xz = self.Wire('xz')
    yz = self.Wire('yz')
    xy_or_xz = self.Wire('xy_or_xz')

    self.AndGate(x, y, xy)  
    self.AndGate(x, z, xz)  
    self.Andgate(x, z, yz)

    # OR(xy,xz,yz) = OR( OR(xy,xz),  yz)
    self.OrGate(xy, xz, xy_or_xz)
    self.OrGate(xy_or_xz, yz, o)

    return 'ok'

def TwoSwitches(self, x, y, o):
    """ An example: light controlled by 2 switches (Rosen, 12.3, Example 3,
        - Figure 6, p. 825)

        F(x, y) = xy + !x.!y
    """
    # Wires x, y, and o are passed as parameters.
    # Only the internal wires need to be created:
    xy = self.Wire('xy')
    not_x = self.Wire('not_x')
    not_y = self.Wire('not_y')
    notx_noty = self.Wire('notx_noty')

    self.AndGate(x,y,xy)
    self.Inverter(x, not_x)
    self.Inverter(y, not_y)
    self.AndGate(not_x, not_y, notx_noty)
    self.OrGate(xy, notx_noty, o)       

    return 'ok'

# This function needs to be defined: parameter, body definition
def HalfAdder(self, x, y, s, c):
            notx_and_y=self.wire('notx_and_y')
            x_and_noty=self.wire('x_and_noty')
            cwire=self.wire('cwire')
            allwire=self.wire(allwire)
            self.OrGate(self.AndGate(not x,y,notx_and_y),self.AndGate(x,not y,x_and_noty),allwire)
    cwire=self.AndGate(x,y,cwire)
    c=cwire
    s=allwire
    pass

def FullAdder(self,x,y,c_i,s, c_out):
    #TODO
    pass

Answer 1

半加器

可以使用与门和异或门实现半加器：

  x    y
  |    |
  |------------------\
  |    |--------\    |
+--------+    +--------+
|  AND   |    |  XOR   |
+--------+    +--------+
    |             |
    c             s

所以实现是这样的：

def Xor(self, x, y, xor):
    nx = self.Wire('nx')
    ny = self.Wire('ny')
    self.Inverter(x,nx)
    self.Inverter(x,ny)
    a1 = self.Wire('a1')
    a2 = self.Wire('a2')
    self.AndGate(nx,y,a1)
    self.AndGate(x,ny,a2)
    self.OrGate(a1,a2,xor)
    pass

def HalfAdder(self, x, y, s, c):
    self.AndGate(x,y,c)
    self.Xor(x,y,s)

全加器

有几种构建 全加器的方法 ，一种方法是使用两个半加器，就像我在 digital electronics 上的课程文本中解释的那样（荷兰语，抱歉):

      x    y          c_i
      |    |           |
    +--------+         |
  /-|   HA   |         |
  | +--------+         |
  |     |              |
  |     `---------\    |
  |               |    |
  |             +--------+
  |    /--------|   HA   |
  |    |        +--------+
+--------+           |
|   OR   |           s
+--------+
    |
  c_out

在 HalfAdder、x 和 y 的顶部，左侧是 c，底部是 s。

所以这意味着：

def FullAdder(self,x,y,c_i,s, c_out):
    ha1s = self.Wire('ha1s')
    ha1c = self.Wire('ha1c')
    self.HalfAdder(x,y,ha1s,ha1c)
    ha2c = self.Wire('ha2c')
    self.HalfAdder(ha1s,c_i,s,ha2c)
    self.OrGate(ha1c,ha2c,c_out)
    pass

一条一般性建议是，始终将问题拆分为您可以更轻松控制的更小的子问题。

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