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| 8-INPUT PRIORITY ENCODERS WITH 3-STATE OUTPUTS The SN54 / 74LS348 and the SN54 / 74LS848 are eight input priority encoders which provide the 8-line to 3-line function. The outputs (A0 - A2) and inputs (0 - 7) are active low. The active low input which has the highest priority (input 7 has the highest) is represented on the outputs (output A0 is the lowest bit). An example would be if inputs 1, 2 and 4 were low, then a binary 4 would be represented on the outputs. The GS (Group Signal) output is active low when any of the inputs are low. It serves to indicate when any of the inputs are active. A0, A1 and A2 are three-state outputs. This allows for up to 64 line expansion without the need for special external circuitry. A logical one on the Enable Input (EI) forces A0, A1 ared A2 to the disabled state and outputs GS and EO to the high state. A high on all data inputs (0 - 7) together with a low on the EI input disables outputs A0, A1, and A2 and forces output GS to the high state and output EO to the low state. Use of the EI input in conjunction with the EO output provides for the capability of having priority encoding of n input signals. The LS848 has special internal circuitry providing for a greatly reduced negative going glitch on the GS (Group Signal) output and on a reduced tendency for the A0, A1 and A2 outputs to become momentarily enabled. Both of these occurrences happen when the EI input goes from a logical one to a logical zero and all data inputs (0 - 7) are held at logical ones. The internal glitch reduction circuitry does add an additional fan-in of one on all data inputs (compared to that of the LS348). OUTPUTS VCC 16 EO 15 EO 4 5 6 7 EI A2 GS 14 GS 3 13 3 INPUTS 2 12 2 1 11 1 0 10 0 A0 A1 OUTPUT A0 9 SN54/74LS348 SN54/74LS848 8-INPUT PRIORITY ENCODERS WITH 3-STATE OUTPUTS LOW POWER SCHOTTKY J SUFFIX CERAMIC CASE 620-09 16 1 16 1 N SUFFIX PLASTIC CASE 648-08 16 1 D SUFFIX SOIC CASE 751B-03 ORDERING INFORMATION SN54LSXXXJ SN74LSXXXN SN74LSXXXD 8 GND Ceramic Plastic SOIC 1 4 2 5 3 6 INPUTS 4 7 5 EI 6 A2 7 A1 OUTPUTS FUNCTION TABLE INPUTS EI H L L L L L L L L L 0 X H X X X X X X X L 1 X H X X X X X X L H 2 X H X X X X X L H H 3 X H X X X X L H H H 4 X H X X X L H H H H 5 X H X X L H H H H H 6 X H X L H H H H H H 7 X H L H H H H H H H A2 Z Z L L L L H H H H OUTPUTS A1 Z Z L L H H L L H H A0 Z Z L H L H L H L H GS H H L L L L L L L L EO H L H H H H H H H H H = HIGH Logic Level L = LOW Logic Level X = Irrelevant Z = High Impedance State FAST AND LS TTL DATA 5-1 SN54/74LS348 * SN54/74LS848 BLOCK DIAGRAMS (5) EI (10) 0 (15) EO (14)GS G1 G13 G29 1 (11) G2 G31 G14 (12) (9) A0 (13) 3 (1) (2) (3) (4) 6 (6) A2 7 (4) G8 (3) G7 G12 G24 G25 G26 G27 G28 (6) A2 (7) A1 4 (1) 2 (12) G3 G9 (13) G4 G15 G16 G17 G10 G19 G20 5 6 7 (2) G6 G11 G21 G22 G23 (7) A1 G18 (9) A0 G30 (15) EO (14) GS (5) EI (10) 0 1 2 3 4 5 (11) G5 SN54 / 74LS348 SN54 / 74LS848 GUARANTEED OPERATING RANGES Symbol VCC TA IOH IOH IOL IOL Supply Voltage Operating Ambient Temperature Range Output Current -- High Output Current -- High Output Current -- Low Output Current -- Low EO, GS A0, A1, A2 A0, A1, A2 EO, GS A0, A1, A2 A0, A1, A2 Parameter 54 74 54 74 54, 74 54 74 54 74 54 74 Min 4.5 4.75 - 55 0 Typ 5.0 5.0 25 25 Max 5.5 5.25 125 70 - 0.4 - 1.0 - 2.6 4.0 8.0 12 24 Unit V C mA mA mA mA FAST AND LS TTL DATA 5-2 SN54/74LS348 * SN54/74LS848 DC CHARACTERISTICS OVER OPERATING TEMPERATURE RANGE (unless otherwise specified) Limits Symbol S bl VIH VIL VIK Parameter P Input HIGH Voltage 54 Input LOW Voltage 74 Input Clamp Diode Voltage Output HIGH Voltage A0, A1, A2 VOH EO, GS EO, GS VOL Output LOW Voltage p g EO, GS Output LOW Voltage p g A0, A1, A2 Output Off Current HIGH Output Off Current LOW Input HIGH Current Input 0, EI -- LS348 Input 0 -- LS848 Other -- LS348 Other -- LS848 IIH Input HIGH Current Input 0, EI -- LS348 Input 0 -- LS848 Other -- LS348 Other -- LS848 Input LOW Current Input 0, EI -- LS348 IIL Input 0 -- LS848 Other -- LS348 Other -- LS848 Short Circuit Current (Note 1) EO, GS , A0, A1, A2 Power Supply Current Total, Output HIGH ICC Total, Output LOW 13 25 - 20 - 30 12 54, 74 54 74 54, 74 74 54, 74 74 2.4 2.5 2.7 - 0.65 3.1 3.5 3.5 0.25 0.35 0.25 0.35 0.4 0.5 0.4 0.5 20 -20 20 40 40 60 0.1 0.2 0.2 0.3 - 0.4 - 0.8 - 0.8 - 1.2 - 120 - 130 23 mA VCC = MAX, Inputs 7, EI = GND All Others Open 0.8 - 1.5 V V V V V V V V A A A A A A mA mA mA mA mA mA mA mA mA mA VCC = MAX All Inputs and Outputs Open VCC = MAX VIN = 0.4 V MAX, 04 VCC = MAX VIN = 7.0 V MAX, 70 VCC = MAX VIN = 2.7 V MAX, 27 IOL = 4.0 mA IOL = 8.0 mA IOL = 12 mA IOL = 24 mA VCC = VCC MIN, VIN = VIL or VIH per Truth Table VCC = VCC MIN, VIN = VIL or VIH per Truth Table Min 2.0 0.7 V Typ Max Unit Ui V Test C di i T Conditions Guaranteed Input HIGH Voltage for All Inputs Guaranteed Input LOW Voltage for p g All Inputs VCC = MIN, IIN = - 18 mA VCC = MIN, IOH = MAX, VIN = VIH or VIL per Truth Table VOL IOZH IOZL VCC = MAX, VOUT = 2.7 V VCC = MAX, VOUT = 0.4 V IOS VCC = MAX Note 1: Not more than one output should be shorted at a time, nor for more than 1 second. FAST AND LS TTL DATA 5-3 SN54/74LS348 * SN54/74LS848 AC CHARACTERISTICS (VCC = 5.0 V, TA = 25C) From (Input) 1 thru 7 To (Output) A0, A0 A1 or A2 output Out-of-Phase 1 thru 7 A0, A0 A1 or A2 output EI A0, A0 A1 or A2 24 Out-of-Phase 0 thru 7 E0 output In-Phase 0 thru 7 GS output In-Phase EI GS output In-Phase EI EO output EI A0, A0 A1 or A2 23 35 23 35 25 18 40 27 30 18 45 27 ns CL = 5.0 p pF RL = 667 14 17 36 21 14 17 36 21 ns 9.0 11 21 17 9.0 11 21 17 ns 26 38 40 55 26 38 40 55 ns CL = 15 pF pF RL = 2.0 11 41 18 24 11 41 18 ns 23 25 35 39 23 25 35 39 ns 20 23 30 35 20 23 30 35 ns CL = 45 pF pF RL = 667 LS348 Limits Waveform W f In-Phase Min Typ 11 Max 17 Min LS848 Limits Typ 12 Max 18 ns Unit Ui Test C di i Conditions T Symbol S bl tPLH tPHL tPLH tPHL tPZH tPZL tPLH tPHL tPLH tPHL tPLH tPHL tPLH tPHL tPHZ tPLZ FAST AND LS TTL DATA 5-4 |
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