diff --git a/pymlac/test_CPU.py b/pymlac/test_CPU.py
new file mode 100644
index 0000000..1886d1c
--- /dev/null
+++ b/pymlac/test_CPU.py
@@ -0,0 +1,171 @@
+#!/usr/bin/env python
+# -*- coding: utf-8 -*-
+
+"""
+Test pymlac CPU opcodes DIRECTLY.
+
+Usage: test_CPU.py [<options>] <filename>
+
+where <filename> is a file of test instructions and
+      <options> is one or more of
+          -h    prints this help and stops
+"""
+
+# We implement a small interpreter to test the CPU.  The test code is read in
+# from a file:
+#
+#    # LAW                                                                            
+#    setreg ac 012345; setreg l 1; setreg pc 0100; setmem 0100 [LAW 0]; RUN; checkcycles 1; checkreg pc 0101; checkreg ac 0
+#    setreg ac 012345; setreg l 0; setmem 0100 [LAW 0]; RUN 0100
+#            checkcycles 1; checkreg pc 0101; checkreg ac 0
+#
+# The instructions are delimited by ';' characters.  A line beginning with a
+# TAB character is a continuation of the previous line.
+# Lines with '#' in column 1 are comments.
+#
+# The test instructions are:
+#     setreg <name> <value>
+#         where <name> is one of AC, L or PC, value is any value
+#         (all registers are set to 0 initially)
+#
+#     setmem <addr> <value>
+#         where <addr> is an address and value is any value OR
+#         [<instruction>] where the value is the assembled opcode
+#
+#     run [<addr>]
+#         execute one instruction, if optional <addr> is used PC := addr before
+#
+#     checkcycles <number>
+#         check number of executed cycles is <number>
+#
+#     checkreg <name> <value>
+#         check register (AC, L or PC) has value <value>
+#
+#     checkmem <addr> <value>
+#         check that memory at <addr> has <value>
+#
+#     allreg <value>
+#         sets all registers to <value>
+#         a "allreg 0" is assumed before each test
+#
+#     allmem <value>
+#         sets all of memory to <value>
+#         a "allmem 0" is assumed before each test
+#
+# In addition, all of memory is checked for changed values after execution
+# except where an explicit "checkmem <addr> <value>" has been performed.
+# Additionally, registers that aren't explicitly checked are tested to make
+# sure they didn't change.
+#
+# If a test line finds no error, just print the fully assembled test line.
+# If any errors are found, print line followed by all errors.
+
+
+import MainCPU
+import Memory
+
+
+def setreg(name, value):
+    """Set register to a value.
+
+    Remember value to check later.
+    """
+
+    global RegValues
+    
+    RegValues[name] = value
+    exec "MainCPU.%s = %07o" % (name, value)
+
+def setmem(addr, value):
+    """Set memory location to a value."""
+
+    global MemValues
+
+    MemValues[addr] = value
+    Memory.memory[addr] = value
+
+
+def allmem(value):
+    """Set all of memory to a value.
+
+    Remember value to check later.
+    """
+
+    global MemAllValue
+
+    MemAllValue = value
+    for mem in range(Memory.MAXMEM):
+        Memory.memory[mem] = value
+
+def allreg(value):
+    """Set all registers to a value."""
+
+    global RegAllValue
+
+    RegAllValue = value
+    MainCPU.AC = value
+    MainCPU.L = value & 1
+    MainCPU.PC = value
+
+def execute(test):
+    """Execute test string in 'test'."""
+
+    global RegValues, MemValues
+    global RegAllValue, MemAllValue
+
+    # set globals
+    RegValues = {}
+    MemValues = {}
+    RegAllValue = {}
+    MemAllValue = {}
+
+    # clear memory and registers to 0 first
+    memset(0)
+    regset(0)
+
+    # interpret the test instructions
+    instructions = test.split(';')
+    for op in instructions:
+        print op
+
+
+
+
+def main(filename):
+    """Execute CPU tests from 'filename'."""
+
+    # get all tests from file
+    with open(filename, 'rb') as fd:
+        lines = fd.readlines()
+
+    # read lines, join continued, get complete tests
+    tests = []
+    test = ''
+    for line in lines:
+        line = line[:-1]        # strip newline
+
+        if line[0] == '#':      # a comment
+            continue
+
+        if line[0] == '\t':     # continuation
+            if test:
+                test += '; '
+            test += line[1:]
+        else:                   # beginning of new test
+            if test:
+                tests.append(test)
+            test = line
+
+    # flush last test
+    if test:
+        tests.append(test)
+
+    # now do each test
+    for test in tests:
+        execute(test)
+
+
+################################################################################
+
+if __name__ == '__main__':
+    main('CPU.test')