similarity-memory

name	similarity-memory
description	Use when working with memory IC similarity calculations - comparing EEPROM/Flash MPNs, understanding I2C/SPI interface matching, equivalent groups across manufacturers, or memory-specific similarity logic.

Memory Similarity Calculator Skill

Guidance for working with MemorySimilarityCalculator in the lib-electronic-components library.

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For metadata-driven similarity architecture, see /similarity-metadata:

• SpecImportance levels (CRITICAL, HIGH, MEDIUM, LOW, OPTIONAL)
• ToleranceRule types (exactMatch, percentageTolerance, minimumRequired, etc.)
• SimilarityProfile contexts (DESIGN_PHASE, REPLACEMENT, COST_OPTIMIZATION, etc.)
• Calculator integration patterns and gotchas

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Overview

The MemorySimilarityCalculator compares memory ICs based on:

• Equivalent groups - Cross-manufacturer equivalents
• Memory type - EEPROM, Flash, etc.
• Interface - I2C, SPI
• Capacity - Must match for high similarity
• Voltage range - Operating voltage compatibility

Applicable Types

ComponentType.MEMORY
// Any type starting with "MEMORY_"
// Returns true for null to handle unrecognized memory devices

Similarity Thresholds

HIGH_SIMILARITY = 0.9;   // Equivalent parts
MEDIUM_SIMILARITY = 0.7; // Same type/interface, close specs
LOW_SIMILARITY = 0.3;    // Different capacity or interface

I2C EEPROM Equivalents

Capacity	Equivalent Parts
256Kbit	24LC256, AT24C256, M24C256, CAT24C256
512Kbit	24LC512, AT24C512, M24C512, CAT24C512
1Mbit	24LC1024, AT24C1024, M24C1024

calculator.calculateSimilarity("24LC256", "AT24C256", registry);
// Returns >= 0.7 (equivalent I2C EEPROMs)

SPI EEPROM Equivalents

Capacity	Equivalent Parts
256Kbit	25LC256, 25AA256, AT25256, M95256
512Kbit	25LC512, 25AA512, AT25512, M95512

SPI Flash Equivalents

Capacity	Equivalent Parts
32Mbit	W25Q32JV, W25Q32FW, MX25L3233F, S25FL032P, IS25LP032
64Mbit	W25Q64JV, W25Q64FW, MX25L6433F, S25FL064P, IS25LP064
128Mbit	W25Q128JV, W25Q128FW, MX25L12833F, S25FL128, IS25LP128

calculator.calculateSimilarity("W25Q32JV", "MX25L3233F", registry);
// Returns >= 0.3 (same capacity SPI Flash)

Interface Rules

I2C and SPI memory have lower similarity due to different interfaces:

calculator.calculateSimilarity("24LC256", "25LC256", registry);
// Returns <= 0.7 (same capacity, different interface)

Capacity Rules

Different capacities return LOW_SIMILARITY:

calculator.calculateSimilarity("W25Q32JV", "W25Q128JV", registry);
// Returns 0.3 (same family, different size)

Package Handling

Package codes don't significantly affect similarity for memory:

• Same memory, different package = HIGH_SIMILARITY (0.9)
• Same memory, compatible package = HIGH_SIMILARITY (0.9)
• Same memory, different package type = ~0.8

Manufacturer Prefixes

Prefix	Manufacturer	Type
24LC	Microchip	I2C EEPROM
AT24C	Atmel/Microchip	I2C EEPROM
M24C	ST	I2C EEPROM
CAT24C	ON Semi	I2C EEPROM
25LC/25AA	Microchip	SPI EEPROM
AT25	Atmel/Microchip	SPI EEPROM
M95	ST	SPI EEPROM
W25Q	Winbond	SPI Flash
MX25L	Macronix	SPI Flash
S25FL	Spansion/Cypress	SPI Flash
IS25LP	ISSI	SPI Flash

Test Examples

// Same I2C EEPROM
calculator.calculateSimilarity("24LC256", "24LC256", registry);
// Returns 1.0

// Cross-manufacturer I2C EEPROM
calculator.calculateSimilarity("24LC256", "AT24C256", registry);
// Returns >= 0.7

// Same Flash, different manufacturer
calculator.calculateSimilarity("W25Q64JV", "MX25L6433F", registry);
// Returns >= 0.3

// Different capacity
calculator.calculateSimilarity("24LC256", "24LC512", registry);
// Returns 0.3

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Metadata-Driven Implementation (January 2026)

Status: ✅ Converted (PR #117)

The MemorySimilarityCalculator now uses a metadata-driven approach with spec-based comparison.

Specs Compared

Spec	Importance	Tolerance Rule	Description
memoryType	CRITICAL	exactMatch	EEPROM, Flash, SRAM, etc.
capacity	CRITICAL	exactMatch	256Kbit, 512Kbit, 1Mbit, etc.
interface	HIGH	exactMatch	I2C, SPI, Parallel
package	LOW	exactMatch	SOIC, DIP, TSSOP, etc.

Implementation Pattern

// Short-circuit check for CRITICAL incompatibility
if (!memoryType1.isEmpty() && !memoryType2.isEmpty() && !memoryType1.equals(memoryType2)) {
    return LOW_SIMILARITY;
}
if (!capacity1.isEmpty() && !capacity2.isEmpty() && !capacity1.equals(capacity2)) {
    return LOW_SIMILARITY;
}

// Weighted spec scoring
// memoryType: CRITICAL (1.0 weight)
// capacity: CRITICAL (1.0 weight)
// interface: HIGH (0.7 weight)
// package: LOW (0.2 weight)

Behavior Changes

Comparison	Legacy Result	Metadata Result	Notes
24LC256 vs 24LC256	1.0	1.0	Identical
24LC256 vs AT24C256	0.7+	0.85	Equivalent I2C EEPROM
W25Q32JV vs MX25L3233F	0.3+	0.61	Same capacity Flash
24LC256 vs 24LC512	0.3	0.3	Short-circuit on capacity
W25Q32JVSSIQ vs W25Q32JVSFIQ	0.7+	0.93	Same Flash, different package

Why more accurate: Metadata approach prioritizes capacity and type matching, with interface as secondary concern.

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Learnings & Quirks

Part Number Patterns

• 24xx = I2C interface, 25xx = SPI interface
• C often indicates CMOS
• Capacity in Kbits: 256 = 32KB, 512 = 64KB, 1024 = 128KB

Revision Suffixes

• JV, FW, JW on Winbond = package/voltage variants
• A, B, C suffixes = revisions (usually compatible)

Voltage Compatibility

• Standard: 2.7V-5.5V
• Low voltage: 1.7V-3.6V (check compatibility)