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HD74HC149

Hitachi Semiconductor
Part Number HD74HC149
Manufacturer Hitachi Semiconductor
Description 8-to-8-line Priority Encoder
Published Mar 23, 2005
Detailed Description HD74HC149 8-to-8-line Priority Encoder Description The HD74HC149 is priority encoder which has 8 input lines (0 - 7) an...
Datasheet PDF File HD74HC149 PDF File

HD74HC149
HD74HC149

Overview
HD74HC149 8-to-8-line Priority Encoder Description The HD74HC149 is priority encoder which has 8 input lines (0 - 7) and 8 output lies (Y0 - Y7).
It is the logical combination of a HD74HC148 8-3 line priority encoder driving a HD74HC138 3-8 line decoder.
Only one request output can be low at a time.
The output that is low is dependent on the highest priority request that is low.
The order of priority is 7 highest and 0 lowest.
When E input is high, all outputs are high.
When a output (Y0 - Y 7) is low, P output is low and this indicates active condition.
Features • • • • • High Speed Operation: tpd (0 - 7 to Y) = 16 ns typ (CL = 50 pF) High Output Current: Fanout of 10 LSTTL Loads Wide Operating Voltage: VCC = 2 to 6 V Low Input Current: 1 µA max Low Quiescent Supply Current: ICC (static) = 4 µA max (Ta = 25°C) HD74HC149 Function Table Inputs 0 X H X X X X X X X L H : L : X : 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 E H L L L L L L L L L Outputs Y0 H H H H H H H H H L Y1 H H H H H H H H L H Y2 H H H H H H H L H H Y3 H H H H H H L H H H Y4 H H H H H L H H H H Y5 H H H H L H H H H H Y6 H H H L H H H H H H Y7 H H L H H H H H H H P H H L L L L L L L L High level Low level Irrelevant Pin Arrangement 0 1 2 3 Inputs 4 5 6 7 E 1 2 3 4 5 6 7 8 9 20 VCC 19 Y0 18 Y1 17 Y2 16 Y3 15 Y4 14 Y5 13 Y6 12 Y7 11 P (Top view) Outputs GND 10 2 HD74HC149 Logic Diagram 7 Y7 6 Y6 5 Y5 4 Y4 3 Y3 2 Y2 1 Y1 0 Y0 P E 3 HD74HC149 DC Characteristics Ta = 25°C Item Input voltage Symbol VIH Ta = –40 to +85°C Max — — — 0.
5 1.
35 1.
8 — — — — — 0.
1 0.
1 0.
1 0.
33 0.
33 ±1.
0 40 µA µA I OL = 4 mA I OL = 5.
2 mA Vin = VCC or GND Vin = VCC or GND, Iout = 0 µA V I OH = –4 mA I OH = –5.
2 mA Vin = VIH or VIL I OL = 20 µA V Vin = VIH or VIL I OH = –20 µA V Unit V Test Conditions VCC (V) Min Typ Max Min 2.
0 4.
5 6.
0 1.
5 — 3.
15 — 4.
2 — — — — — — — — — — 0.
5 1.
5 3.
15 4.
2 — VIL 2.
0...


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