Microchip Technology 24LCS21A/P

Overview

24LCS21A/P from Microchip Technology Inc. is a 128 × 8-bit dual-mode I²C™-compatible serial EEPROM designed for monitor identification and EDID™ storage in display systems. It operates in Transmit-Only mode (DDC1™) with VCLK clocking and Bidirectional mode (DDC2™/I²C) with SCL clocking, supports 2.5–5.5V supply, features hardware write-protection via WP pin, and delivers 1 mA active current and 10 μA standby current at 5.5V.

For engineers reviewing the 24LCS21A/P datasheet, 24LCS21A/P pinout, 24LCS21A/P application, or 24LCS21A/P equivalent, key selection considerations include DDC1/DDC2 mode switching behavior, VCLK vs. SCL clock domain separation, WP fuse activation logic at address 7Fh, page-write buffer limits (8 bytes), and industrial temperature range (–40°C to +85°C) compliance.

Technical Context

The 24LCS21A/P implements two independent communication protocols on shared SDA: Transmit-Only mode uses VCLK for unidirectional EDID™ streaming (MSB-first, 8-bit bytes + null bit), while Bidirectional mode uses SCL for standard I²C™ read/write with slave address 1010000X. Mode transition requires a valid high-to-low SCL edge followed by detection of control byte '1010000X' within 128 VCLK pulses.

Write protection is implemented via dual mechanisms: WP pin functionality is disabled until any data is written to address 7Fh (fuse set), after which WP state and VCLK logic level jointly determine R/W access per Table 6-1; VCLK must be held high during command/data transfer to enable writes in Bidirectional mode, and is ignored during self-timed 10 ms write cycles.

Key Specifications

Pinout & Package

24LCS21A/P is supplied in an 8-pin Plastic Dual In-line Package (PDIP), 300 mil body width, with through-hole mounting compatibility and industrial temperature rating.

Key Features

Applications

Equivalent & Alternatives

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

Compared with AT24C02D-SSHM-T and 24LC024T-I/SN, the 24LCS21A/P uniquely integrates DDC1™ transmit autonomy with I²C™ bidirectional programmability in one device, eliminating external timing logic and enabling true plug-and-play monitor identification without host processor involvement.

Availability

24LCS21A/P is available at Aetrix Electronics and suitable for monitor EDID™ storage, display configuration management, DDC bus recovery systems, and industrial HMI display modules requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for 24LCS21A/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 U.S.-based semiconductor manufacturer specializing in microcontrollers, analog devices, and memory products for embedded control applications.

The 24LCS21A/P belongs to Microchip's DDC-compliant serial EEPROM product line, engineered specifically for video display interface standards including VESA DDC1™ and DDC2™ to simplify monitor identification and configuration in PC, consumer, and industrial display systems.

FAQ

What is the primary function of the VCLK pin on the 24LCS21A/P?

The VCLK pin on the 24LCS21A/P serves as the clock input for Transmit-Only mode (DDC1™), synchronizing EDID™ bitstream output on the SDA line. In Bidirectional mode, it acts as a write-enable control: VCLK must be held high to permit writes, and its logic level combines with the WP pin state to determine memory access rights after fuse activation at address 7Fh. The 24LCS21A/P will not accept write commands unless VCLK is asserted high during command/data transfer phases.

How does the 24LCS21A/P switch between Transmit-Only and Bidirectional modes?

The 24LCS21A/P powers up in Transmit-Only mode and remains there as long as SCL is held high. A valid high-to-low transition on SCL initiates Transition mode, during which the device monitors the I²C™ bus for its slave address (1010000X). If detected within 128 VCLK pulses, it enters Bidirectional mode permanently until power is cycled. If no address is received, it reverts to Transmit-Only mode. This behavior is intrinsic to the 24LCS21A/P and requires no external configuration.

Can the 24LCS21A/P be used as a drop-in replacement for standard I²C™ EEPROMs like the 24LC01B?

No, the 24LCS21A/P is not a drop-in replacement for standard I²C™ EEPROMs such as the 24LC01B. While it supports I²C™ in Bidirectional mode, the 24LCS21A/P includes dedicated VCLK and mode-switching logic, dual clock domains, and DDC1™-specific initialization that are absent in generic EEPROMs. Its pinout differs (VCLK and NC pins replace A0/A1 address inputs), and its memory map and write-protection scheme are application-optimized for display systems - using it in non-DDC designs requires careful validation of timing and control signal routing.

What happens if the WP pin is left unconnected on the 24LCS21A/P?

If the WP pin is left unconnected (open) on the 24LCS21A/P, its behavior depends on fuse state: before writing to address 7Fh, the WP pin has no effect and the device remains fully writable when VCLK = 1. After fuse activation, an open WP pin is interpreted as logic high per Table 6-1, enabling read/write access provided VCLK is also high. However, Microchip recommends explicit pull-up or pull-down to avoid indeterminate states - leaving WP floating post-fuse may risk intermittent write failures in noisy environments.

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

Yes, the 24LCS21A/P supports page write operations with an 8-byte internal page buffer. Up to eight data bytes can be loaded into the buffer before issuing a Stop condition, after which all bytes are written simultaneously during the self-timed 10 ms internal cycle. Page boundaries align to 8-byte intervals (addresses 00h–07h, 08h–0Fh, etc.), and crossing a boundary causes wraparound within the current page - this constraint is enforced in hardware and applies exclusively to the 24LCS21A/P's physical memory architecture.