MC5474F182 Datasheet, PDF (4/4 Pages) Motorola, Inc – CARRY LOOKAHEAD GENERATOR

MC54/74F182
AC CHARACTERISTICS (Continued)
54/74F
54F
74F
TA = +25°C
VCC = +5.0 V
CL = 50 pF
TA = –55°C to +125°C
VCC = 5.0 V ± 10%
CL = 50 pF
TA = 0°C to +70°C
VCC = 5.0V ± 10%
CL = 50 pF
Symbol
Parameter
Min Typ Max
Min
Max
Min
Max
Unit
tPLH
tPHL
tPLH
tPHL
tPLH
tPHL
Propagation Delay
P1, P2, or P3 to G
Propagation Delay
Gn to G
Propagation Delay
Pn to P
2.0
7.9
10
2.0
12.5
2.0
11
ns
2.0
6.0
8.0
2.0
9.5
2.0
9.0
2.0
8.3 10.5
2.0
12.5
2.0
11.5
ns
1.5
5.7
7.5
1.5
9.5
1.5
8.5
2.5
5.7
7.5
2.5
11
2.5
8.5
ns
2.5
4.1
5.5
2.5
7.5
2.5
6.5
FUNCTIONAL DESCRIPTION
The F182 carry lookahead generator accepts up to four
pairs of active-LOW Carry Propagate (P0-P3) and carry Gen-
erate (G0-G3) signals and an active-HIGH Carry input (Cn) and
provides anticipated active-HIGH carries (Cn _{+ x,} Cn _{+ y,} Cn _{+ z)}
across four groups of binary adders. The F182 also has ac-
tive-LOW Carry Propagate (P) and Carry Generate (G) out-
puts which may be used for further levels of lookahead. The
logic equations provided at the output are:
Cn _{+ x} = G0 + P0Cn
Cn _{+ y} = G1 + P1G0 + P1P0Cn
Cn _{+ z} = G2 + P2G1 + P2P1G0 + P2P1P0Cn
G = G3 + P3G2 + P3P2G1 + P3P2P1G0
P = P3P2P1P0
Also, the F182 can be used with binary ALUs in an active-
LOW or active-HIGH input operand mode. The connections
(Figure 1) to and from the ALU to the carry lookahead genera-
tor are identical in both cases. Carries are rippled between
lookahead blocks. The critical speed path follows the circled
numbers. There are several possible arrangements for the
carry interconnects, but all achieve about the same speed. A
28-bit ALU is formed by dropping the last F181 or F381.
A, B
1
CnALCUn**+GP4
Cn _{ALU** G}
P
Cn _{ALU** G}
P
2
Cn _{ALU** G}
P
C16
CnALUCn**+G4
P
CnALU** _G
P
5
Cn Cn _{+ 4}
ALU**
Cn Cn _{+ 4} ^COUT
ALU** (C32)
F⁶
P0 G0 P1 G1 P2G2 P3 G3
P0 G0 P1G1 P2 G2 P3G3
CIN
Cn
F182
G
Cn
F182
G
Cn _{+ x} Cn _{+ y} Cn _{+ zP 3}
Cn _{+ x} Cn _{+ y} Cn _{+ zP}
4
** ALUs may be either F181, F381, or 2901A.
Figure 1. 32-Bit ALU with Ripple Carry Between 16-Bit Lookahead ALUs
FAST AND LS TTL DATA
4-100