STMicroelectronics M74HC688RM13TR

Overview

M74HC688RM13TR from STMicroelectronics is a high-speed CMOS 8-bit equality comparator with symmetrical output drive (|IOH| = IOL ≥ 4 mA), 17 ns typical propagation delay at 6 V, and wide 2–6 V operating voltage range. It performs bit-wise comparison of two 8-bit words (P0–P7 vs. Q0–Q7) and asserts active-low P=Q output when matched - used in address decoding, bus arbitration, and digital system state validation.

For engineers reviewing the M74HC688RM13TR datasheet, M74HC688RM13TR pinout, M74HC688RM13TR application, or M74HC688RM13TR equivalent, key selection criteria include enable-controlled cascading for >8-bit comparisons, guaranteed noise immunity (VNIH/VNIL ≥ 28% VCC), and TSSOP-20 packaging for space-constrained logic interfaces.

Technical Context

The M74HC688 implements combinational equality detection using silicon gate C2MOS technology, with fully buffered inputs and outputs. Its single active-low enable (G) allows hierarchical word-length extension by gating the P=Q output of upstream comparators.

All 18 signal pins are ESD-protected, and propagation delays are balanced (tPLH ≅ tPHL) across input-to-output paths. The device operates over –55°C to +125°C with rail-to-rail input/output voltage compatibility (VI, VO = 0 to VCC).

Key Specifications

Pinout & Package

TSSOP-20 package: 6.5 mm × 4.4 mm body, 0.65 mm pitch, exposed pad not electrically connected, JEDEC MO-153 compliant.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar 8-bit equality comparator applications.

Compared with SN74HC688N and 74VHC688M, the M74HC688RM13TR offers optimal balance of compact TSSOP-20 packaging, industry-leading noise immunity (28% VCC), and proven reliability across extended temperature ranges - making it preferred for production-grade industrial and automotive control modules.

Availability

M74HC688RM13TR is available at Aetrix Electronics and suitable for memory address decoding, bus arbitration logic, industrial PLC I/O mapping, and digital test equipment pattern matching requiring stable component supply across automotive, industrial automation, and embedded computing programs.

Supply support for M74HC688RM13TR includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

STMicroelectronics is a global semiconductor leader headquartered in Geneva, designing and manufacturing analog, digital, and mixed-signal ICs for automotive, industrial, and consumer markets.

The M74HC688 belongs to ST's high-speed HC logic family, engineered for pin-compatible upgrades from legacy TTL while delivering lower power, wider voltage range, and enhanced ESD robustness in industrial control and instrumentation.

FAQ

Can M74HC688RM13TR operate at 3.3 V?

Yes. The device is fully specified from 2 V to 6 V, including 3.3 V operation. At VCC = 3.3 V, VIH = 2.31 V min., VIL = 0.99 V max., and tPD ≈ 30 ns typ., meeting standard 3.3 V CMOS interface requirements without level translation.

Is the P=Q output truly open-drain?

No. P=Q is a push-pull output with symmetrical drive (|IOH| = IOL ≥ 4 mA), not open-drain. It actively drives HIGH and LOW. External pull-up is unnecessary unless interfacing with higher-voltage logic families requiring wired-OR functionality.

How is cascading implemented with multiple M74HC688 devices?

Cascade by connecting the P=Q output of one device to the G (enable) input of the next. All G inputs must be tied LOW except the first stage. Only when all upstream stages assert P=Q LOW will the final stage's output reflect full-word equality.

Does M74HC688RM13TR require decoupling capacitors?

Yes. A 100 nF ceramic capacitor must be placed between VCC (pin 20) and GND (pin 10), located within 10 mm of the device. This suppresses switching noise and ensures stable operation at maximum speed, especially under heavy capacitive loading.