Homework #4
ECE 422
Dr. R. Roosta
Microprogramming
Design a number format that satisfies these requirements and uses as few bits as possible.
Indicate clearly the number codes used and why they were chosen.
1) Design a minimal length multiple encoded fields micro instruction format with the
following set of micro instructions under the constraint that each encoded field must
activate at most one control signal at any time.
Micro-instruction
Control Signa1s
I1
a, b, c, h
I2
a, c, e, g
I3
a, d, f
I4
b, c, f, g
2) A CPU has 16 registers. an ALU with 16 logic and 16 arithmetic functions and a
shifter with 8 operations, all connected with a common bus system.
a) Formulate a control word to specify the various micro operations for the CPU.
b) Specify the number of bits for each field and give a general encoding scheme for each.
c) Show the bits of a control word that specify the micro operation: R7 ← R1 + R14.
3) The micro-instructions stored in the control memory have a width of 24
bits. Each microinstruction is divided into three fields: a micro operation field of 13
bits, a next address field, and a MUX select field There are eight status in the inputs of
the multiplexer.
a) How many bits are there in the MUX select field?
b) How many bits are there in the next address field?
c) What is the size of the control memory?
d) How many bits are there in the control address register?
e) Draw a detailed block diagram of the circuit showing all inter-connections between
the blocks.
Homework #4
EE 422
Dr. R. Roosta
4) Add the following instruction to the computer defined in secnon7.3. Obtain the
symbolic micro-program for each routine as in Table 1-1.
Symbol Opcode Symbolic Function
AND
0011 AC ← AC ∩ M
XCHG 0100 AC ← M, M ← AC
SUB
0101 AC ← AC − M
ADM
0110 M ← M + AC
BTCL
0111
AC ← AC ∩ M’
BZ
1000
SEQ
1001
BPNZ
1010
if (AC = 0) then
PC ← EA
if (AC = M) then
PC ← PC +1
If ( AC > 0) then
PC ← EA
Description
AND M to AC
Exchange AC and M
Subtract M from AC
Add AC to memory operand
(AC does not change)
AND complemented memory
word to AC (BIT clear)
Branch if AC is zero
Skip if AC equals M
(AC does not change)
Branch if AC is positive and
non-zero
*EA is the effective address; M is the memory word stored at the effective address
5) Assume that the input logic of the micro_program sequencer of text book has four inputs, I2, I1,
I0 and T and three outputs S1, S0, and L. The operations that can be performed in
follows:
I1 I2 I3
Operation
x 0 0
Increment CAR unconditionally
0 0 1
JMP to ADF if T = 1, increment CAR if T = 0
1 0 1
Call subroutine if T = 1, increment CAR if T = 0
0 1 0
Return from subroutine if T = 1, increment CAR if T = 0
1 1 0
MAP external address if T = 1, increment CAR if T = 0
x 1 1
JMP to ADF unconditionally
Design the input logic circuit using a minimum number of gates.
the unit are as