CD4532 8-bit priority encoder: specs and pinout
A CMOS 8-bit priority encoder: it converts the highest-priority active input among D7-D0 into a 3-bit binary code on Q2-Q0 (D7 has the highest priority, D0 the lowest). GS goes high when any input is active; EO goes high when none is, so chips can be cascaded.
Specs
| Spec | Value | Source |
|---|---|---|
| Function | 8 inputs D7-D0 to 3-bit binary Q2-Q0; D7 highest priority. Chip-enable input EI: the encoder is inhibited when EI is low and enabled when EI is high; Group Select GS is high when one or more inputs are active; Enable-Out EO is high when no input is active and low when any input is high | source Page 1 (3-307), description and functional diagram |
| Supply voltage range | 3 V to 18 V (recommended, full package temperature range); absolute maximum -0.5 V to +20 V | source Page 1, Recommended Operating Conditions and Maximum Ratings |
| Input levels (VDD = 5 V) | VIL 1 V max; VIH 4 V min at the -55 to +125 C limits (3.5 V min at +25 C) | source Page 2 (3-308), Static Electrical Characteristics |
| Output drive at 5 V, 25 C | Sink (IOL) 0.51 mA min at VO 0.4 V; source (IOH) -0.51 mA min at VO 4.6 V; VOL 0.05 V max, VOH 4.95 V min | source Page 2, Static Electrical Characteristics |
| Input current | +/-0.1 uA max at 18 V (+25 C); input capacitance 5 pF typ | source Page 2, Static and Dynamic Electrical Characteristics |
| Propagation delay Dn to Qm (25 C) | 220 ns typ / 440 ns max at VDD 5 V; 110/220 ns at 10 V; 85/160 ns at 15 V | source Page 2, Dynamic Electrical Characteristics |
| Quiescent current at 25 C | 0.04 uA typ, 5 uA max at VDD 5 V | source Page 2, Static Electrical Characteristics |
| Operating temperature | -55 C to 125 C | source Page 1 Maximum Ratings; Package Option Addendum |
Power
| Value | Source | |
|---|---|---|
| Supply | 3 V to 18 V DC (recommended) | source Page 1 Recommended Operating Conditions; page 2 Static Electrical Characteristics |
| Current | Quiescent 0.04 uA typ, 5 uA max per package at VDD 5 V, 25 C (static; no output load) | source Page 1 Recommended Operating Conditions; page 2 Static Electrical Characteristics |
Pinout
Bare DIP-16 logic IC; the pin table is the chip's own terminal assignment (TI/Harris SCHS082C, Oct 2003).
| Pin | Function | Voltage | Notes | Source |
|---|---|---|---|---|
| 1 | D4 | Input | source Page 1, Terminal Assignment (top view) | |
| 2 | D5 | Input | source Page 1, Terminal Assignment (top view) | |
| 3 | D6 | Input | source Page 1, Terminal Assignment (top view) | |
| 4 | D7 | Input; highest priority | source Page 1, Terminal Assignment (top view) | |
| 5 | EI | Chip enable input; high = enabled, low = inhibited | source Page 1, Terminal Assignment (top view) | |
| 6 | Q2 | Binary output | source Page 1, Terminal Assignment (top view) | |
| 7 | Q1 | Binary output | source Page 1, Terminal Assignment (top view) | |
| 8 | VSS | Ground | source Page 1, Terminal Assignment (top view) | |
| 9 | Q0 | Binary output | source Page 1, Terminal Assignment (top view) | |
| 10 | D0 | Input; lowest priority | source Page 1, Terminal Assignment (top view) | |
| 11 | D1 | Input | source Page 1, Terminal Assignment (top view) | |
| 12 | D2 | Input | source Page 1, Terminal Assignment (top view) | |
| 13 | D3 | Input | source Page 1, Terminal Assignment (top view) | |
| 14 | GS | Group select output; high when one or more inputs are active | source Page 1, Terminal Assignment (top view) | |
| 15 | EO | Enable-out; high when no input is active | source Page 1, Terminal Assignment (top view) | |
| 16 | VDD | Positive supply, 3 V to 18 V recommended | source Page 1, Terminal Assignment (top view) |
Build with it
Project ideas for the CD4532 8-bit priority encoder. Each link opens Soldr with the prompt filled in; Soldr assigns the pins, checks power and shows how to wire every part.
- Eight-key priority keypad: Eight buttons with pull-down resistors feed D0-D7; Q2-Q0 and GS go to Uno pins. Run the chip at the Uno's 5 V so the 5 V logic levels in the datasheet apply; EI is tied to VDD (high), because the encoder is inhibited when EI is low.
- Quiz-game priority display: The encoder resolves simultaneous presses in hardware (highest number wins); the Uno reads Q2-Q0 and shows the number. Learning project: priority is fixed by D7 to D0, not by who pressed first. EI is tied to VDD (high) to enable the encoder.
- Sixteen-input cascade: The datasheet describes EO as high when no input is active and low when any input is high, which disables the lower stage. The top chip's EI is tied to VDD (high) and its EO drives the lower chip's EI. This needs two CD4532 chips; read both chips' Q and GS lines on the Uno.
- Interrupt-driven event logger: GS is high whenever any input is active (EI tied to VDD, high), so one microcontroller pin can serve as an interrupt while Q2-Q0 give the highest-priority source. The outputs are not latched: Q2-Q0 are valid only while an input is held, so the Uno must read them before the button is released. Buttons stand in for switches or sensor outputs that are already at 5 V logic.
Common mistakes
- Driving a 5 V-supplied CD4532 directly from 3.3 V logic: at VDD 5 V the datasheet needs VIH of 3.5 V min (4 V at the temperature extremes), so a 3.3 V output is below the specified high level. Match the chip's VDD to the logic or level-shift the inputs (source: link, page 2).
- Leaving an input floating: the datasheet tests one input at a time with all others at VDD or VSS, so tie unused inputs to a defined level (source: link, page 2 note).
- Using the outputs to drive loads: source/sink is only about 0.5 mA minimum at 5 V, 25 C, so read the outputs with a microcontroller or buffer instead of driving LEDs or relays directly (source: link, page 2).
Not covered by the official source
- The datasheet pages are scanned images with no text layer, so the pin table and limits are transcribed by hand.
- Datasheet limits are given at 5, 10 and 15 V only; behaviour at a 3.3 V supply is not specified beyond the 3 V minimum recommended supply.
- The cascade idea needs a second CD4532 (the same part twice).
Sources
- link (TI CD4532B Types, data sheet acquired from Harris Semiconductor, SCHS082C revised Oct 2003)