Microchip Technology AT24C21-10SC-2.5

Overview

AT24C21-10SC-2.5 from Atmel (now Microchip) is a 1K-bit (128 × 8) two-wire serial EEPROM with dual-mode operation: Transmit-only Mode (DDC1™ compliant) and Bidirectional Mode (DDC2™ compliant). It operates from 2.5V to 5.5V, supports 100 kHz clock frequency at 2.5V, features 8-byte page write capability, and delivers 1 million write cycles with 100-year data retention - deployed in monitor identification and embedded configuration storage.

For engineers reviewing the AT24C21-10SC-2.5 datasheet, AT24C21-10SC-2.5 pinout, AT24C21-10SC-2.5 application, or AT24C21-10SC-2.5 equivalent, key selection considerations include VCLK/SCL dual-clock architecture, DDC1/DDC2 mode switching behavior, 2.5V low-voltage timing compliance, write protection via VCLK-to-GND, and JEDEC SOIC-8 package compatibility with industrial temperature range (-40°C to +85°C).

Technical Context

The AT24C21-10SC-2.5 implements a unique dual-clock interface: VCLK drives continuous serial output in Transmit-only Mode (e.g., EDID streaming), while SCL enables standard I²C-compatible bidirectional read/write in DDC2 mode. Mode transition occurs only once per power cycle - a valid high-to-low edge on SCL switches from Transmit-only to Bidirectional Mode permanently until reset.

Internally organized as 128 words of 8 bits, it uses 7-bit addressing with no A0/A1/A2 pins (all NC), supports byte and 8-byte page writes with self-timed 10 ms max write cycle, and includes Schmitt-triggered, noise-filtered inputs plus built-in low-VCC write inhibition below 1.5V.

Key Specifications

Pinout & Package

AT24C21-10SC-2.5 is housed in an 8-lead JEDEC SOIC package (8S1), 0.150" wide, gull-wing lead form, RoHS-compliant, rated for industrial temperature range (-40°C to +85°C).

Key Features

Applications

Equivalent & Alternatives

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

Compared with AT24C21-10SC-2.5, AT24C02C-SSHM-T offers higher density and speed but forfeits DDC1 mode and VCLK-based EDID streaming; M24C01-RMN6TP matches density and package but lacks dual-clock architecture and 2.5V DDC1 timing compliance - neither is drop-in compatible for monitor identification use cases.

Availability

AT24C21-10SC-2.5 is available at Aetrix Electronics and suitable for monitor identification, embedded configuration storage, and legacy VGA interface support requiring stable component supply, industrial temperature tolerance, and DDC1/DDC2 dual-mode capability.

Supply support for AT24C21-10SC-2.5 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

Atmel Corporation, acquired by Microchip Technology in 2016, designs high-reliability nonvolatile memory and microcontroller solutions for industrial, automotive, and computing markets.

The AT24C21 belongs to Atmel's legacy 2-wire serial EEPROM family, engineered specifically for display interface compliance (DDC1/DDC2) and low-voltage embedded configuration storage - not general-purpose I²C EEPROMs.

FAQ

What is the primary function of the VCLK pin on the AT24C21-10SC-2.5?

The VCLK pin on the AT24C21-10SC-2.5 serves as the clock input for Transmit-only Mode (DDC1), triggering serial bit output on SDA at each rising edge. It also enables hardware write protection when tied to GND in Bidirectional Mode. Unlike SCL, VCLK is ignored after mode transition unless required to enable write operations - making it essential for EDID streaming and fail-safe configuration locking in the AT24C21-10SC-2.5.

Does the AT24C21-10SC-2.5 support standard I²C communication?

Yes, the AT24C21-10SC-2.5 supports standard I²C communication in Bidirectional Mode, using SCL and SDA pins with device address 0b1010xxx (where xxx are don't-care bits). It complies with I²C timing at 100 kHz up to 5.5V and down to 2.5V, including START/STOP conditions, ACK polling, and 8-byte page writes - all fully functional in the AT24C21-10SC-2.5 when operating outside Transmit-only Mode.

How does the AT24C21-10SC-2.5 handle power-up and mode initialization?

On power-up, the AT24C21-10SC-2.5 defaults to Transmit-only Mode and remains there until a valid high-to-low transition occurs on SCL. During initialization, the starting address (00H or 7FH) is determined by SDA state during the first eight VCLK cycles. No external reset is needed - mode persistence is power-cycle dependent, and the AT24C21-10SC-2.5 requires no configuration registers or firmware to enter either operational mode.

Can the AT24C21-10SC-2.5 be used in place of a standard 1K I²C EEPROM like the 24LC01B?

No - the AT24C21-10SC-2.5 is not a drop-in replacement for standard 1K I²C EEPROMs such as the 24LC01B. It lacks A0/A1/A2 address pins (all NC), uses a dual-clock architecture (VCLK+SCL), and requires mode-aware firmware to manage DDC1/DDC2 transitions. While pin-compatible in SOIC-8, its functional behavior, timing, and protocol differ fundamentally - substituting it without redesign risks EDID failure or write lockup in the AT24C21-10SC-2.5.

What is the significance of the "-10SC-2.5" suffix in AT24C21-10SC-2.5?

The "-10SC-2.5" suffix in AT24C21-10SC-2.5 specifies three attributes: "10" denotes 10 ms maximum write cycle time; "SC" indicates 8-lead JEDEC SOIC package (8S1); and "-2.5" confirms guaranteed operation from 2.5V to 5.5V supply, including full 100 kHz timing compliance at 2.5V - distinguishing it from wider-voltage or faster variants and confirming industrial temperature rating (-40°C to +85°C) per the ordering table.