Homework 3

                       Due Wednesday, May 18.



In this assignment you will build a scaled-down version of MIC-1,
to be called SUBMIC-1.

The differences between SUBMIC-1 and MIC-1 are:

   1.  Only 4 registers, and each is only 4 bits wide.
   2.  No shifter, mar, mbr, rd, wr.
   3.  MIC-1 memory words consist only of 2+2+1+3*2+8 = 19 bits
       (alu,cond,enc,a,b,c,addr). 

You are REQUIRED to use tri-state devices to connect the registers
to the a and b buses.

I suggest you organize your work as follows:

     I.  Build the ALU.  Test it.
    II.  Extend the ALU to a register file/buses/ALU complex.
	 Test it.
   III.  Build an MPC/MIR/MUX complex.  Test it.
    IV.  Integrate everything together.

Be VERY careful in your final testing.  Write a SUBMIC-1 program 
for this purpose; it should be short, maybe 5 or 10 instructions,
but should be a reasonably general test.  (The Reader will also
write his own program, which he will use in grading your submission.)

You can generate some test values in your registers with various
microinstructions as follows.  The registers will start at 0000, so
a microinstruction that does inversion will give you 1111, i.e. -1.
Adding the latter quantity to itself will give you -2, i.e. 1110,
and inverting that will give you 1, i.e. 0001.  Etc.

I have revised the Chipmunk mini-manual.  The main revisions, most
of which are relevant to the current assignment, are:

   a.  Discussion of tri-state devices.
   b.  Description of the SRAM8K device.
   c.  Multimodule pages and files.
   d.  Correction of an error in the description of Probe mode.
   e.  Some new points in the Miscellaneous section.

This assignment is not conceptually deep, but obviously there are
a lot of little details to work out, many of which will take some
significant time.  Thus it is crucial that you start your work NOW;
if you do, you should have no problem finishing on time.