24LCS21AT-I/SN

Memory IC Overview

The Microchip Technology 24LCS21AT-I/SN is a 1Kb (128 x 8-bit) dual-mode Electrically Erasable PROM. It operates on a single supply voltage ranging from 2.5V to 5.5V and supports I2C-compatible interfaces with clock frequencies of up to 100 kHz at 2.5V and 400 kHz at 5V. The device features a hardware write-protect pin, a page-write buffer for eight bytes, and ensures 1,000,000 erase/write cycles with data retention exceeding 200 years. It is housed in an 8-pin SOIC package and rated for industrial temperatures from -40°C to +85°C.

Memory IC Feature Summary

• Implements DDC1/DDC2 interface standards for monitor identification with automatic recovery to DDC1 mode
• Supports bidirectional I2C communication and unidirectional transmit-only operation via VCLK
• Includes flexible hardware write protection controlled by the WP pin and internal fuse logic

Memory IC Applications

• Monitor identification and configuration storage
• Display Data Channel (DDC) applications
• Storage of serial transmission control information

Memory IC Procurement Notes

Verify that the 'T' suffix confirms tape-and-reel packaging and the 'I' suffix specifies the industrial temperature range. Confirm the 'SN' designation matches the required 8-pin SOIC physical footprint. Ensure the specific revision aligns with current design requirements as older variants may have different thermal or electrical characteristics.

Memory IC Selection Notes

Select this component when dual-mode operation between standard I2C and DDC protocols is necessary. It is suitable for designs requiring low standby power and robust noise protection through Schmitt Trigger inputs. Consider the page-write buffer size if high-speed sequential writing is required within memory boundaries.

Memory IC Part Context

This part belongs to the 24LCS21A family of dual-mode serial EEPROMs designed specifically for display and monitor applications. It complements standard I2C memory devices by adding specialized transition logic for EDID and DDC compliance while maintaining standard serial bus compatibility.

Memory IC Replacement Considerations

The 24LC21AT-I/SN serves as a functional substitute but lacks the dedicated DDC1/DDC2 dual-mode capabilities and VCLK pin functionality required for monitor identification applications.

Memory IC FAQ

How does the device switch between modes?

The device powers up in Transmit-Only mode. A valid high-to-low transition on the SCL pin triggers Transition mode, where it searches for a control byte to enter Bidirectional mode permanently until power is removed.

What is the function of the VCLK pin in Bidirectional mode?

In Bidirectional mode, VCLK acts as a write-enable control. Holding VCLK high allows normal write operations, while holding it low prevents writing to the memory array.