======================================================================== 74F521 8-BIT IDENTITY COMPARATOR ======================================================================== Family: Fairchild FAST (Advanced Schottky TTL) Source: 1985 Fairchild FAST Data Book, pages 4-375 ... 4-377. The 1980 data book carries the 'F521 in its Section 3 selection guide only (page 3-34, description and logic symbol). Status: Released data sheet Ratings: Vcc = +5.0 V +/-5%, TA = 0 to +70 deg C DESCRIPTION ----------- The 'F521 is an expandable 8-bit comparator. It compares two words of up to eight bits each and provides a LOW output when the two words match bit for bit. The expansion input /IA=B also serves as an active LOW enable input. o Compares Two 8-Bit Words in 6.5 ns Typ o Expandable to Any Word Length o 20-Pin Package CONNECTION DIAGRAM (20-pin DIP) ------------------------------- Pin Function Pin Function --- ------------------------ --- ------------------------ 1 /IA=B Expansion/Enable 20 Vcc 2 A0 Word A bit 0 19 /OA=B Identity output 3 B0 Word B bit 0 18 B7 Word B bit 7 4 A1 Word A bit 1 17 A7 Word A bit 7 5 B1 Word B bit 1 16 B6 Word B bit 6 6 A2 Word A bit 2 15 A6 Word A bit 6 7 B2 Word B bit 2 14 B5 Word B bit 5 8 A3 Word A bit 3 13 A5 Word A bit 5 9 B3 Word B bit 3 12 B4 Word B bit 4 10 GND 11 A4 Word A bit 4 The A and B inputs alternate along the package so that each bit pair (An, Bn) sits on adjacent pins. TRUTH TABLE ----------- Inputs Output -------------- ------ /IA=B A, B /OA=B ----- ------ ------ L A = B* L L A =/= B H H A = B* H H A =/= B H H = HIGH voltage level; L = LOW voltage level. *A0 = B0, A1 = B1, A2 = B2, etc. INPUT LOADING / FAN-OUT ----------------------- Pin Names Description U.L. HIGH/LOW ---------- --------------------------------------- ------------- A0 - A7 Word A Inputs 0.5 / 0.375 B0 - B7 Word B Inputs 0.5 / 0.375 /IA=B Expansion or Enable Input (Active LOW) 0.5 / 0.375 /OA=B Identity Output (Active LOW) 25 / 12.5 DC CHARACTERISTICS OVER OPERATING TEMPERATURE RANGE --------------------------------------------------- Symbol Parameter Min Typ Max Units Conditions ------ -------------------- --- --- --- ----- ---------------- ICC Power Supply Current 21 32 mA Vcc = Max All inputs HIGH AC CHARACTERISTICS ------------------ TA = +25 C 74F Vcc = +5.0V TA/Vcc = Com Symbol Parameter CL Min Typ Max Min Max Units ------ ----------------------------- ----- --- ---- --- --- ---- ----- tPLH Prop Delay An or Bn to /OA=B 50 pF 3.5 7.0 10.0 3.5 11.0 ns tPHL Prop Delay An or Bn to /OA=B 50 pF 4.5 7.0 10.0 4.0 11.0 ns tPLH Prop Delay /IA=B to /OA=B 50 pF 3.0 5.0 6.5 3.0 7.5 ns tPHL Prop Delay /IA=B to /OA=B 50 pF 3.5 6.5 9.0 3.5 10.0 ns