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74F181PC
54F181,74F181 54F181 74F181 4-Bit Arithmetic Logic Unit Literature Number: SNOS164A Logic Symbols Active-HIGH Operands Active-LOW Operands TL F 9491–3 IEEE IEC TL F 9491 – 4 Unit Loading Fan Out 54F 74F OC-Open Collector 10 30 10 30 10 40 10 10 10 50 50 33 3 OC 33 3 50 33 3 50 33 3 50 33 3 20 mA b1 8 mA 20 mA b1 8 mA 20 mA b2 4 mA 20 mA b0 6 mA 20 mA b3 0 mA b 1 mA 20 mA 20 mA b 1 mA 20 mA b 1 mA 20 mA b 1 mA 20 mA TL F 9491 – 10 e A Operand Inputs (Active LOW) B Operand Inputs (Active LOW) Function Select Inputs Mode Control Input Carry Input Function Outputs (Active LOW) Comparator Output Carry Generate Output (Active LOW) Carry Propagate Output (Active LOW) Carry Output UL Input IIH IIL HIGH LOW Output IOH IOL bs ol A 0 – A3 B 0 – B3 S0 – S3 M Cn F0 – F3 AeB G P Cn a 4 Description et Pin Names Functional Description each group of four ’F181 devices Carry lookahead can be provided at various levels and offers high speed capability over extremely long word lengths The A e B output from the device goes HIGH when all four F outputs are HIGH and can be used to indicate logic equivalence over four bits when the unit is in the Subtract mode The A e B output is open collector and can be wired AND with other A e B outputs to give a comparison for more than four bits The A e B signal can also be used with the Cn a 4 signal to indicate AlB and AkB The Function Table lists the arithmetic operations that are performed without a carry in An incoming carry adds a one to each operation Thus select code LHHL generates A minus B minus 1 (2s complement notation) without a carry in and generates A minus B when a carry is applied Because subtraction is actually performed by complementary addition (1s complement) a carry out means borrow thus a carry is generated when there is no underflow and no carry is generated when there is underflow As indicated this device can be used with either active LOW inputs producing active LOW outputs or with active HIGH inputs producing active HIGH outputs For either case the table lists the operations that are performed to the operands labeled inside the logic symbol O The ’F181 is a 4-bit high-speed parallel Arithmetic Logic Unit (ALU) Controlled by the four Function Select inputs (S0 – S3) and the Mode Control input (M) it can perform all the 16 possible logic operations or 16 different arithmetic operations on Active HIGH or Active LOW operands The Function Table lists these operations When the Mode Control input (M) is HIGH all internal carries are inhibited and the device performs logic operations on the individual bits as listed When the Mode Control input is LOW the carries are enabled and the device performs arithmetic operations on the two 4-bit words The device incorporates full internal carry lookahead and provides for either ripple carry between devices using the Cn a 4 output or for carry lookahead between packages using the signals P (Carry Propagate) and G (Carry Generate) In the Add mode P indicates that F is 15 or more while G indicates that F is 16 or more In the Subtract mode P indicates that F is zero or less while G indicates that F is less than zero P and G are not affected by carry in When speed requirements are not stringent the ’F181 can be used in a simple Ripple Carry mode by connecting the Carry output (Cn a 4) signal to the Carry input (Cn) of the next unit For high speed operation the device is used in conjunction with a carry lookahead circuit One carry lookahead package is required for 2
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