RT level combinational blocks Paolo PRINETTO Politecnico di Torino (Italy) University of Illinois at Chicago, IL (USA) Lecture 5.1

2 5.1 Goal  This lecture presents the set of functional blocks that are usually considered to be “elementary” or “basic” at the RT level.

3 5.1 Prerequisites  Lecture 3.3

4 5.1 Homework  No particular homework is foreseen

5 5.1 Further readings  Students interested in making a reference to a text book on the arguments covered in this lecture can refer, for instance, to:  M. Morris Mano, C.R.Kime: “Logic and Computer Design Fundamentals,” 2nd edition updated Prentice Hall, Upple Saddle River, NJ (USA), 2001, (chapter 3, pp )

6 5.1 Elementary functional blocks Multiplexer Adder- Subtracter Decoder Encoder Comparator ROM ALU Multiplier 1’s counter I/O interfaces

7 5.1 Adders We shall consider:  half adder  full adder  adder-subtracter

8 5.1 Half-Adder A half-adder has:  2 inputs A i, B i  2 outputs S i and C i+1 and computes the binary sum of the 2 input bits, providing:  the sum S i  the carry C i+1

9 5.1 S i = A i  B i C i+1 = A i  B i A i B i C i+1 S i

Full-Adder A full-adder has:  3 inputs A i, B i and C i  2 outputs S i and C i+1 and computes the binary sum of the 3 input bits, providing:  the sum S i  the carry C i+1

S i = A i  B i  C i C i+1 = A i B i + A i C i + B i C i = = A i B i + ( A i  B i ) C i  A i B i C i C i+1 S i

Adder-subtracter An adder-subtracter is a combinational block capable of adding/subtracting two n-bits inputs operands, detecting overflow conditions. It has  2 n-bits data inputs, both labeled from n-1 to 0  1 control input to select one of the two operations  1 n-bits data output  1 control output asserted when an overflow condition is occurred.

Adder-subtracter Adder-subtracter (cont’d) FUNC(n-1 downto 0) A(n-1 downto 0) B(n-1 downto 0) ADD/~SUB OVFL Symbol

Elementary functional blocks Adder- Subtracter Decoder Encoder Comparator ROM ALU Multiplier 1’s counter I/O interfaces Multiplexer

Multiplexer A multiplexer is a combinational block capable of forcing its output to the current value of one of its inputs, according to the values of some control signals. Each input can be either a single wire or a bus.

Multiplexer A multiplexer has:  2 k data inputs, labeled from 2 k -1 to 0  k control inputs  1 data output. k 2 k -1 2 k MUX … It gets the value present on the input labeled 2 i, where i (0  i  k-1) is the binary number present on the control inputs.

OUT SEL(k-1 downto 0) Multiplexer (cont'd) Symbol IN(2 k -1 downto 0)

Multiplexer (cont’d) Symbol M0(n-1 downto 0) OUT(n-1 downto 0) M1(n-1 downto 0) M2(n-1 downto 0) M2 k -1(n-1 downto 0) SEL(k-1 downto 0)

Elementary functional blocks Multiplexer Adder- Subtracter Decoder Encoder Comparator ROM ALU Multiplier 1’s counter I/O interfaces

Decoder A decoder k  2 k has:  1 n-bit data input  2 n outputs, labeled from 0 to 2 n -1  1 enable. When enabled, just the output labeled 2 j is active, where j is the value present on the data input. When disabled, no output is active.

Decoder (cont’d) Symbol DOUT(0) DIN(n-1 downto 0) ENABLE DOUT(1) DOUT(2) DOUT(2 n -1)

Elementary functional blocks Multiplexer Adder- Subtracter Decoder Encoder Comparator ROM ALU Multiplier 1’s counter I/O interfaces

Priority Encoder A priority encoder has:  2 k inputs, labeled from 0 to 2 k -1 (each input is assigned a fixed priority)  k outputs  1 “data valid” output  1 enable.

Priority Encoder (cont’d)  When enabled:  the outputs get the value j, where j is the label of the highest priority asserted input  the “data valid” output is asserted.  When disabled or when no input is asserted:  the “data valid” output is not asserted.

M0 CODE(n-1 downto 0) ENABLE M1 M2 M2 n -1 Priority Encoder (cont’d) VALID Symbol

Elementary functional blocks Multiplexer Adder- Subtracter Decoder Encoder Comparator ROM ALU Multiplier 1’s counter I/O interfaces

Comparator A comparator gets 2 n-bit binary numbers:  A(n-1 downto 0)  B(n-1 downto 0) and provides in output the result of the comparison between A and B. A control input UM/~2C specifies whether the input operands are unsigned or signed, respectively.

Comparator (cont’d) A B AeqBAneBAltBAgtBAleBAgeB Symbol B(n-1 downto 0) A(n-1 downto 0) UM/~2C Sel

Elementary functional blocks Multiplexer Adder- Subtracter Decoder Encoder Comparator ROM ALU Multiplier 1’s counter I/O interfaces

Counter of 1’s occurrences A counter of 1’s occurrences has:  1 n-bit data input  1 m-bit data output, being m =  log 2 n . The device counts the number of occurrences of a ‘1’ on its inputs and provides it on its outputs.

Counter of 1’s occurrences Counter of 1’s occurrences (cont’d) Symbol DIN(n-1 downto 0) 1’s C DOUT(m-1 downto 0)

Elementary functional blocks Multiplexer Adder- Subtracter Decoder Encoder Comparator ROM ALU Multiplier 1’s counter I/O interfaces

ROM A 2 k  n ROM (Read-Only Memory) has:  k address inputs  n data outputs  2 k n-bit internal cells, storing permanent values. The outputs gets the value stored in the j cell, j being the current value present on address inputs.

ROM (cont’d) ADDR D_OUT Symbol ADDR(2 k -1 downto 0) DATA(n-1 downto 0)

Elementary functional blocks Multiplexer Adder- Subtracter Decoder Encoder Comparator ROM ALU Multiplier 1’s counter I/O interfaces

ALU An n-bit ALU (Arithmetic Logic Unit) performs logic and/or arithmetic operations on 2 n-bit operands, under the control of ad-hoc control signals.

ALU (cont’d) FUNC(n-1 downto 0) CONTROL C_IN C_OUT STATUS Symbol B(n-1 downto 0) A(n-1 downto 0)

F=A  B F=A  B' Functions implemented by the ALU ’181 InputFunctions S3S2S1S0arithmetic (M=0)logic (M=1) F=A minus 1 plus CIN F=AB minus 1 plus CIN F=AB' minus 1 plus CIN F=1111 plus CIN F=A plus (A+B') plus CIN F=AB plus (A+B') plus CIN F=A minus B minus 1 plus CIN F=A+B' plus CIN F=A plus (A+B) plus CIN F=A plus B plus CIN F=AB' plus (A+B) plus CIN F=A+B plus CIN F=A plus A plus CIN F=AB plus A plus CIN F=AB' plus A plus CIN F=A plus CIN F=A' F=A'+ B' F=A'+ B F= 1111 F=A'B' F=B' F=A+B' F=A'B F=B F=A+B F=0000 F=AB' F=AB F=A

Elementary functional blocks Multiplexer Adder- Subtracter Decoder Encoder Comparator ROM ALU Multiplier 1’s counter I/O interfaces

Multiplier A multiplier has:  1 n-bits data inputs, labeled from n-1 to 0  1 m-bits data inputs, labeled from m-1 to 0  no control signals  k-bits data outputs, labeled from k-1 to 0 and provides in output the results of the product between the two input operands.

Multiplier (cont’d) MUL_OUT(k-1 downto 0) * B(n-1 downto 0) A(m-1 downto 0) Symbol

Multiplier (cont’d) MUL_OUT(k-1 downto 0) * B(n-1 downto 0) A(m-1 downto 0) Symbol Signed operands: k=m+n- 1Signed operands: k=m+n- 1 Unsigned operands: k=m+nUnsigned operands: k=m+n

Elementary functional blocks Multiplexer Adder- Subtracter Decoder Encoder Comparator ROM ALU Multiplier 1’s counter I/O interfaces

I/O interfaces The combinational interfaces for the following I/O devices will be presented:  led bar driver  7-segments display  dip-switch  keypad.

Led bar interface LED_BAR interface n DATA(n-1 downto 0)

DATA DISPLAY interface 4, 7 DOT ENABLE 7-segments display interface

a b c d e f g BI A B C D a b c d e f g a b c d e f g DOT ENABLE 7-segments display interface

Dip-switch interface DATA DIP_SW interface n n

Keypad interface DATA KEYPAD interface 4, AB CDEF DATA_VALID