diff --git a/register.py b/register.py
index b3b46cd..3454aee 100644
--- a/register.py
+++ b/register.py
@@ -48,10 +48,41 @@ class Register:
 
 
 class Acumulator(Register):
-    positive_flag = False
     negative_flag = False
     zero_flag = False
-    carry = False
+    carry_flag = False
+    parity_flag = False
 
-    def add(self, register):
+    def set_flags(self):
+        self.negative_flag = False
+        self.zero_flag = False
+
+        if self.get_signed() < 0:
+            self.negative_flag = True
+        if self.get() == 0:
+            self.zero_flag = True
+        v = self.get()
+        self.parity_flag = True
+        while v > 0:
+            if (v & 1) == 1:
+                self.parity_flag = not self.parity_flag
+            v >>= 1
+
+    def add(self, register: Register):
+        self.value += register.value
+        if self.value.bit_length() > self.n_bits:
+            self.carry_flag = True
+            self.trucate()
+        self.set_flags()
+
+    def sub(self, register: Register):
+        self.negate()
+        self.add(register)
+        self.negate()
+        self.set_flags()
+
+    def shift_right(self, through_carry=True):
+        pass
+
+    def shift_left(self, through_carry=True):
         pass