Microchip Technology 24LCS21A-I/P

Overview

24LCS21A-I/P from Microchip Technology Inc. is a 128 × 8-bit dual-mode I²C™-compatible serial EEPROM designed for monitor identification (DDC1™/DDC2™) in display systems. It operates from 2.5V to 5.5V, supports both Transmit-Only and Bidirectional modes, features hardware write-protection via WP pin, and delivers 1 mA active current and 10 μA standby current at 5.5V. It is used in EDID storage for LCD monitors and digital displays requiring robust configuration memory with DDC compliance.

For engineers reviewing the 24LCS21A-I/P datasheet, 24LCS21A-I/P pinout, 24LCS21A-I/P application, or 24LCS21A-I/P equivalent, key selection considerations include dual-mode clocking (VCLK for DDC1™, SCL for I²C™), flexible write protection (WP + VCLK logic), guaranteed 1 million erase/write cycles, 200-year data retention, and industrial temperature support (–40°C to +85°C).

Technical Context

The 24LCS21A-I/P implements two distinct operational protocols: Transmit-Only mode uses VCLK as clock input and SDA as unidirectional output for continuous EDID bitstream transmission (MSB-first, 8-bit bytes + null bit), while Bidirectional mode uses SCL/SDA per standard I²C™ protocol with slave address 1010000X. Mode transition occurs only on valid high-to-low SCL edge followed by detection of control byte '1010000X'; recovery to Transmit-Only mode requires 128 consecutive VCLK pulses with idle SCL.

Write protection is implemented via dual mechanisms: factory-default unlocked state until address 7Fh is written (enabling WP pin function), and real-time VCLK-level gating - write enabled only when VCLK = high in Bidirectional mode. Internal self-timed write cycle (10 ms max) includes auto-erase, and page write buffer supports up to eight bytes within a single 8-byte physical page boundary.

Key Specifications

Pinout & Package

8-pin PDIP (Plastic Dual In-line Package), 300 mil body width, through-hole mounting. RoHS-compliant, Pb-free finish.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar serial EEPROM applications.

Compared with 24LCS21A-I/P, the 24LC21A-I/P omits DDC1™ mode and VCLK functionality entirely, limiting it to pure I²C™ use cases; the AT24C128N-10PU-2.7 offers greater capacity and speed but removes all DDC protocol logic, making it unsuitable for monitor identification without significant system-level redesign.

Availability

24LCS21A-I/P is available at Aetrix Electronics and suitable for monitor EDID storage, display configuration memory, DDC bus compliance modules, and industrial display control interfaces requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for 24LCS21A-I/P 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

Microchip Technology Inc. is a leading provider of microcontrollers, analog devices, and memory solutions, headquartered in Chandler, Arizona, with global design and manufacturing operations.

The 24LCS21A-I/P belongs to Microchip's DDC-compliant serial EEPROM product line, engineered specifically for display interface applications requiring seamless integration with VESA DDC1™ and DDC2™ standards in monitor, graphics adapter, and video infrastructure designs.

FAQ

What is the primary function of the 24LCS21A-I/P in display systems?

The 24LCS21A-I/P serves as a dual-mode serial EEPROM for storing and transmitting EDID data in display systems. It operates in Transmit-Only mode (DDC1™) to stream EDID continuously using VCLK, or switches to Bidirectional mode (DDC2™/I²C™) for read/write access via SCL/SDA upon detecting a valid control byte. This enables full VESA DDC compliance without external logic, and the 24LCS21A-I/P is specifically designed to meet the timing and state-machine requirements of the DDC Standard.

How does the write-protection mechanism work on the 24LCS21A-I/P?

The 24LCS21A-I/P implements two-tier write protection: first, the device ships with the WP pin disabled (factory default); writing any value to address 7Fh programs an internal fuse that activates WP functionality. Second, even with WP enabled, writes in Bidirectional mode require VCLK to be held high - pulling VCLK low disables all writes regardless of WP state. This dual-gate design prevents accidental overwrites during normal operation and allows safe EDID read-only deployment, and the 24LCS21A-I/P supports both hardware and protocol-level locking strategies.

Can the 24LCS21A-I/P be used in systems that only support standard I²C™ and not DDC protocols?

Yes, the 24LCS21A-I/P fully supports standard I²C™ operation in Bidirectional mode using slave address 1010000X, with 100 kHz/400 kHz timing compliance, ACK polling, and page write capability. Its I²C™ interface is functionally identical to generic 1 Kbit EEPROMs - the DDC1™ Transmit-Only mode is optional and inactive unless VCLK is driven and SCL remains idle. So in pure I²C™ systems, the 24LCS21A-I/P behaves as a standard EEPROM, and the 24LCS21A-I/P retains full backward compatibility while adding DDC-specific features.

What happens if power is removed while the 24LCS21A-I/P is in Bidirectional mode?

Upon power-up, the 24LCS21A-I/P always initializes in Transmit-Only mode - there is no nonvolatile mode state storage. The device has no internal register to retain "last mode" information; mode selection is purely dynamic and determined by SCL/VCLK activity after reset. Therefore, removing power resets the 24LCS21A-I/P to its default Transmit-Only state, ensuring predictable startup behavior in display systems regardless of prior operational mode, and the 24LCS21A-I/P guarantees deterministic initialization without firmware dependency.

Does the 24LCS21A-I/P support page write operations, and what is the page size?

Yes, the 24LCS21A-I/P supports page write operations with an 8-byte page buffer. Up to eight bytes can be loaded into the buffer and written simultaneously upon receipt of a Stop condition, reducing I²C™ transaction overhead. Physical page boundaries align to addresses 00h–07h, 08h–0Fh, etc., and crossing a boundary causes wraparound within the current page - so software must validate address ranges before initiating multi-byte writes. This page write capability is fully supported in Bidirectional mode, and the 24LCS21A-I/P implements the same timing and acknowledgment behavior as specified in the I²C™ standard.