ECE 448 – FPGA and ASIC Design with VHDL George Mason University

Lab 1

Introduction to Aldec Active HDL

Implementing Combinational Logic in VHDL

Example 1: MLU

Introduction to Aldec Active-HDL

MLU Block Diagram

B

A

NEG_A

NEG_B

IN0

IN1

IN2

IN3 OUTPUT

SEL1

SEL0

MUX_4_1

L0L1

NEG_Y

Y

Y1

A1

B1

MUX_0

MUX_1

MUX_2

MUX_3

Experiment 1

Problem 1

ALU of PIC Microcontroller

Pertinent Components of PIC

Working Register7 0W

000000000100010

11111

777

7

000

0

Register File(32 Registers)

Address

00011 7 000100 7 0

STATUS

00101 7 000110 7 0

00111 7 0

8 Special FunctionRegisters

01000 7 0

24 General PurposeRegisters

Addressing Modes

Immediate mode

ANDLW H’6C’

Direct mode

ANDWF H’12’, 0

W & 0x6C W

W & (0x12) W

Assembly language vs. Machine Code

Assembly language

mnemonic [operands]

ANDLW H’6C’

Machine code

‘000101’ ‘010010’

opcode [operands]

ANDWF H’12’, 0

‘1110’ ‘01101100’

Status Register

STATUS 07

Z DC C

Carry/BorrowDigit Carry (3rd4th bit)ZeroPower-downTime-out

Program Page Preselect

Reserved

Definition of the Status Register Flags (1)

Z = 1 if result = 0 0 otherwise

Zero flag - Z zero result

C = 1 if result > MAX_UNSIGNED or result < 0 0 otherwise

where MAX_UNSIGNED = 28-1 for 8-bit results

Carry flag - C out-of-range for unsigned numbers

Definition of the Status Register Flags (2)

DC = 1 if carry from bit 3 to bit 4 (ADDWF) orno borrow from bit 4 to 3 (SUBWF)

0 otherwise

Digit Carry flag – DC Carry / Borrow between MSB of first hex digit and LSB of second

111 1 0010 0110+ 0001 1100 0100 0010

0010 1110 - 0001 1100 0001 0010

DC = 1

Logic Instructions

1. AND ANDWF W & RF W or RF

ANDLW W & L W

2. Inclusive OR

IORWF W | RF W or RF

IORLW W | L W

3. Exclusive ORXORWF W RF W or RFXORLW W L W

4. Ones ComplementCOMF RF RF

DIR

Z C DC

DIR

IMM

DIR

– –

– –

– –

– –

DIR

IMM

IMM

Arithmetic Instructions

1. AdditionADDWF W + RF W or RF

2. Subtraction SUBWF RF – W W or RF

DIR

3. IncrementINCF RF + 1 RF

4. DecrementDECF RF - 1 RF

DIR

Z C DC

DIR

DIR

– –

– –

Shifts and Rotation Instructions

1. Rotate Left Through Carry RLF

2. Rotate Right Through Carry RRF

3. Swap Nibbles SWAPF RF [7:4] W [3:0] or RF [3:0]

RF [4:0] W [7:4] or RF [7:4]

DIR

DIR

Z C DC

DIR

– –x

– –x

– – –

07

. . .C

07 C. . .

Instruction Summary

Example 2

Mini ALU

opcode

A

B

M

RMini ALU

4

4

4

4

4

Mnemonic Operation Opcode

ADDAB R= A + B 0000

ADDAM R = A + M 0001

SUBAB R = A - B 0010

SUBAM R = A - M 0011

NOTA R = NOT A 0100

NOTB R = NOT B 0101

NOTM R = NOT M 0110

ANDAB R = A AND B 0111

ANDAM R = A AND M 1000

ORAB R = A OR B 1001

ORAM R = A OR M 1010

XORAB R = A XOR B 1011

XORAM R = A XOR M 1100

Block diagram

Example 3

Variable Rotator

Function

C = A <<< B

A – 4-bit data inputB – 2-bit rotation amount

Interface

4

4

2

A

B

C

Block diagram

C

Fixed Shifts in VHDL

A(3)A(2) A(1) A(0)

A(3) A(2) A(1)

A>>1

A_shiftR <= ‘0’ & A(3 downto 1);

‘0’

‘0’

Arithmetic Functions in VHDL (1)

To use arithmetic operations involving

std_logic_vectors you need to include the

following library packages:

library ieee;use ieee.std_logic_1164.all;use ieee.STD_LOGIC_UNSIGNED.ALL;

Arithmetic Functions in VHDL (2)

You can use standard +, - operators

to perform addition and subtraction:

signal A : STD_LOGIC_VECTOR(3 downto 0); signal B : STD_LOGIC_VECTOR(3 downto 0); signal C : STD_LOGIC_VECTOR(3 downto 0);

……

C<= A + B;