======================================================================== 74F138 1-OF-8 DECODER/DEMULTIPLEXER ======================================================================== Family: Fairchild FAST (Advanced Schottky TTL) Source: 1985 Fairchild FAST Data Book, pages 4-45 ... 4-48. The 1980 data book carries the 'F138 in its Section 3 selection guide only (page 3-15, description and logic symbol). Status: Released data sheet Ratings: Vcc = +5.0 V +/-5%, TA = 0 to +70 deg C DESCRIPTION ----------- The 'F138 is a high-speed 1-of-8 decoder/demultiplexer. This device is ideally suited for high-speed bipolar memory chip select address decoding. The multiple input enables allow parallel expansion to a 1-of-24 decoder using just three 'F138 devices or a 1-of-32 decoder using four 'F138 devices and one inverter. o FAST Process for High Speed o Demultiplexing Capability o Multiple Input Enable for Easy Expansion o Active LOW Mutually Exclusive Outputs FUNCTIONAL DESCRIPTION ---------------------- The 'F138 high-speed 1-of-8 decoder/demultiplexer accepts three binary weighted inputs (A0, A1, A2) and, when enabled, provides eight mutually exclusive active LOW outputs (/O0 - /O7). The 'F138 features three Enable inputs, two active LOW (/E1, /E2) and one active HIGH (E3). All outputs will be HIGH unless /E1 and /E2 are LOW and E3 is HIGH. This multiple enable function allows easy parallel expansion of the device to a 1-of-32 (5 lines to 32 lines) decoder with just four 'F138 devices and one inverter (See Figure a). The 'F138 can be used as an 8-output demultiplexer by using one of the active LOW Enable inputs as the data input and the other Enable inputs as strobes. The Enable inputs which are not used must be permanently tied to their appropriate active HIGH or active LOW state. CONNECTION DIAGRAM (16-pin DIP) ------------------------------- Pin Function Pin Function --- -------------------- --- -------------------- 1 A0 Address input 0 16 Vcc 2 A1 Address input 1 15 /O0 Output 0 3 A2 Address input 2 14 /O1 Output 1 4 /E1 Enable input 1 13 /O2 Output 2 5 /E2 Enable input 2 12 /O3 Output 3 6 E3 Enable input 3 11 /O4 Output 4 7 /O7 Output 7 10 /O5 Output 5 8 GND 9 /O6 Output 6 TRUTH TABLE ----------- Inputs Outputs -------------- ------ ---------------------------------------- /E1 /E2 E3 A0 A1 A2 /O0 /O1 /O2 /O3 /O4 /O5 /O6 /O7 --- --- --- -- -- -- --- --- --- --- --- --- --- --- H X X X X X H H H H H H H H X H X X X X H H H H H H H H X X L X X X H H H H H H H H L L H L L L L H H H H H H H L L H H L L H L H H H H H H L L H L H L H H L H H H H H L L H H H L H H H L H H H H L L H L L H H H H H L H H H L L H H L H H H H H H L H H L L H L H H H H H H H H L H L L H H H H H H H H H H H L H = HIGH voltage level; L = LOW voltage level; X = immaterial. INPUT LOADING / FAN-OUT ----------------------- Pin Names Description U.L. HIGH/LOW ---------- -------------------------- ------------- A0 - A2 Address Inputs 0.5 / 0.375 /E1, /E2 Enable Inputs (Active LOW) 0.5 / 0.375 E3 Enable Input (Active HIGH) 0.5 / 0.375 /O0 - /O7 Outputs (Active LOW) 25 / 12.5 DC CHARACTERISTICS OVER OPERATING TEMPERATURE RANGE --------------------------------------------------- Symbol Parameter Min Typ Max Units Conditions ------ -------------------- --- --- --- ----- ---------- ICC Power Supply Current 13 20 mA Vcc = Max 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 to /On 50 pF 3.5 5.6 7.5 3.5 8.5 ns tPHL Prop Delay An to /On 50 pF 4.0 6.1 8.0 4.0 9.0 ns tPLH Prop Delay /E1 or /E2 to /On 50 pF 3.5 5.4 7.0 3.5 8.0 ns tPHL Prop Delay /E1 or /E2 to /On 50 pF 3.0 5.3 7.0 3.0 7.5 ns tPLH Prop Delay E3 to /On 50 pF 4.0 6.2 8.0 4.0 9.0 ns tPHL Prop Delay E3 to /On 50 pF 3.5 5.6 7.5 3.5 8.5 ns