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Faculty of Computer Science CMPUT 229 © 2006 Buses and Memories And Adders

Faculty of Computer Science © 2006 CMPUT 229 Buses and Memories And Adders

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Faculty of Computer Science

CMPUT 229 © 2006

Buses and Memories

And Adders

© 2006

Department of Computing Science

CMPUT 229

Adders

Basic building block is “full adder”

– 1-bit-wide adder, produces sum and carry outputs

X Y Cin S Cout 0 0 0 0 0 0 0 1 1 0 0 1 0 1 0 0 1 1 0 1 1 0 0 1 0 1 0 1 0 1 1 1 0 0 1 1 1 1 1 1

Cout is one if two or moreof the inputs are one.

S is one if an odd numberof inputs are one.

© 2006

Department of Computing Science

CMPUT 229

Full-adder circuit

© 2006

Department of Computing Science

CMPUT 229

Ripple adder

– Speed limited by carry chain

– Faster adders eliminate or limit carry chain

• 2-level AND-OR logic ==> 2n product terms

• 3 or 4 levels of logic, carry lookahead

© 2006

Department of Computing Science

CMPUT 229

A bi-stable circuit

How to control it?

– Control inputs

S-R latch

© 2006

Department of Computing Science

CMPUT 229

D latch

© 2006

Department of Computing Science

CMPUT 229

Functional Units and Buses

Clements, pp. 88

COPYRIGHT 2006 OXFORD UNIVERSITY PRESS ALL RIGHTS RESERVED

© 2006

Department of Computing Science

CMPUT 229

Connection of Systems to a Bus

Clements, pp. 88

COPYRIGHT 2006 OXFORD UNIVERSITY PRESS ALL RIGHTS RESERVED

© 2006

Department of Computing Science

CMPUT 229

Outputs Cannot Simply be Connected Together

Clements, pp. 89

COPYRIGHT 2006 OXFORD UNIVERSITY PRESS ALL RIGHTS RESERVED

© 2006

Department of Computing Science

CMPUT 229

Tri-state Outputs

Clements, pp. 89

COPYRIGHT 2006 OXFORD UNIVERSITY PRESS ALL RIGHTS RESERVED

© 2006

Department of Computing Science

CMPUT 229

Symbols for tri-state buffers

Clements, pp. 90

COPYRIGHT 2006 OXFORD UNIVERSITY PRESS ALL RIGHTS RESERVED

© 2006

Department of Computing Science

CMPUT 229

Interconnections with Tri-state Buffers

Clements, pp. 101

COPYRIGHT 2006 OXFORD UNIVERSITY PRESS ALL RIGHTS RESERVED

IN OUTSELWR

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IN OUTSELWR

IN OUTSELWR

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IN OUTSELWR

IN OUTSELWR

IN OUTSELWR

IN OUTSELWR

IN OUTSELWR

DOUT3 DOUT2 DOUT1 DOUT0

3-to-8decoder

2

1

0

A2

A1

A0

0

1

2

3

4

5

6

7

DIN3 DIN0DIN2 DIN1

WE_LCS_L

OE_L

WR_L

IOE_L

0

1

1

IN OUTSELWR

IN OUTSELWR

IN OUTSELWR

IN OUTSELWR

IN OUTSELWR

IN OUTSELWR

IN OUTSELWR

IN OUTSELWR

IN OUTSELWR

IN OUTSELWR

IN OUTSELWR

IN OUTSELWR

IN OUTSELWR

IN OUTSELWR

IN OUTSELWR

IN OUTSELWR

IN OUTSELWR

IN OUTSELWR

IN OUTSELWR

IN OUTSELWR

IN OUTSELWR

IN OUTSELWR

IN OUTSELWR

IN OUTSELWR

IN OUTSELWR

IN OUTSELWR

IN OUTSELWR

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IN OUTSELWR

IN OUTSELWR

IN OUTSELWR

IN OUTSELWR

DOUT3 DOUT3 DOUT3 DOUT3

3-to-8decoder

2

1

0

A2

A1

A0

0

1

2

3

4

5

6

7

DIN3 DIN3DIN3 DIN3

WE_LCS_L

OE_L

WR_L

IOE_L

0

1

1

IN OUTSELWR

IN OUTSELWR

IN OUTSELWR

IN OUTSELWR

IN OUTSELWR

IN OUTSELWR

IN OUTSELWR

IN OUTSELWR

IN OUTSELWR

IN OUTSELWR

IN OUTSELWR

IN OUTSELWR

IN OUTSELWR

IN OUTSELWR

IN OUTSELWR

IN OUTSELWR

IN OUTSELWR

IN OUTSELWR

IN OUTSELWR

IN OUTSELWR

IN OUTSELWR

IN OUTSELWR

IN OUTSELWR

IN OUTSELWR

IN OUTSELWR

IN OUTSELWR

IN OUTSELWR

IN OUTSELWR

IN OUTSELWR

IN OUTSELWR

IN OUTSELWR

IN OUTSELWR

DOUT3 DOUT3 DOUT3 DOUT3

3-to-8decoder

2

1

0

A2

A1

A0

0

1

2

3

4

5

6

7

DIN3 DIN3DIN3 DIN3

WE_LCS_L

OE_L

WR_L

IOE_L

0

1

1

IN OUTSELWR

IN OUTSELWR

IN OUTSELWR

IN OUTSELWR

IN OUTSELWR

IN OUTSELWR

IN OUTSELWR

IN OUTSELWR

IN OUTSELWR

IN OUTSELWR

IN OUTSELWR

IN OUTSELWR

IN OUTSELWR

IN OUTSELWR

IN OUTSELWR

IN OUTSELWR

IN OUTSELWR

IN OUTSELWR

IN OUTSELWR

IN OUTSELWR

IN OUTSELWR

IN OUTSELWR

IN OUTSELWR

IN OUTSELWR

IN OUTSELWR

IN OUTSELWR

IN OUTSELWR

IN OUTSELWR

IN OUTSELWR

IN OUTSELWR

IN OUTSELWR

IN OUTSELWR

DOUT3 DOUT3 DOUT3 DOUT3

3-to-8decoder

2

1

0

A2

A1

A0

0

1

2

3

4

5

6

7

DIN3 DIN3DIN3 DIN3

WE_LCS_L

OE_L

WR_L

IOE_L

0

1

1