Renesas X1226S8ZT1

Overview

X1226S8ZT1 from Intersil is a 4K-bit (512 × 8) real-time clock/calendar IC with integrated 2-wire™ (I²C-compatible) interface, dual non-volatile alarms, on-chip oscillator compensation, and 512-byte EEPROM. It operates from 2.7–5.5V, draws 1.25µA typical operating current, and maintains timekeeping down to 1.8V during battery backup. It is used in utility meters, HVAC controllers, and network infrastructure equipment for accurate time stamping and configuration storage.

For engineers reviewing the X1226S8ZT1 datasheet, X1226S8ZT1 pinout, X1226S8ZT1 application, or X1226S8ZT1 equivalent, this page delivers verified technical context, validated pin functions, confirmed EEPROM block-lock protection modes, oscillator trim range (±30ppm digital + up to ±146ppm analog), and real-world alarm repeat behavior - all specific to the X1226S8ZT1 SOIC-8 Pb-free variant.

Technical Context

The X1226S8ZT1 integrates a temperature-compensated 32.768kHz crystal oscillator with on-die 64-position digitally controlled trim capacitor and six-bit analog trimming register (ATR), enabling fine frequency adjustment from +116ppm to –37ppm. Its dual alarm system supports match-based triggering on second, minute, hour, day-of-week, date, or month - with repeat mode enabled via IM bit in INT register.

It implements a 2-wire™ interface compliant with I²C standard-mode (400kHz max), featuring open-drain SDA/SCL with slope-controlled pull-down, and supports sequential read/write across separate Clock/Control Register (CCR) and EEPROM memory maps. The PHZ/IRQ pin serves as either programmable frequency output (1Hz/4096Hz/32.768kHz) or active-low interrupt, selected via FO1/FO0 bits at address 0011h.

Key Specifications

Pinout & Package

Package: 8-lead SOIC (150 mil), Pb-free (RoHS-compliant), MDP0027 footprint.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar real-time clock/calendar applications.

Compared with DS1307+T&R and PCF8563T/1,118, the X1226S8ZT1 uniquely combines on-die oscillator compensation, dual nonvolatile alarms, and BlockLock™ EEPROM in a single SOIC-8 package - delivering higher design integration, longer field calibration intervals, and stronger firmware integrity for industrial time-critical systems.

Availability

X1226S8ZT1 is available at Aetrix Electronics and suitable for utility metering, HVAC control systems, and network infrastructure equipment requiring stable component supply, long-term lifecycle support, and RoHS-compliant packaging.

Supply support for X1226S8ZT1 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

Intersil (now part of Renesas Electronics) is a semiconductor company specializing in precision analog, power management, and timing solutions for industrial, communications, and computing markets.

The X1226S8ZT1 belongs to Intersil's RTC+EEPROM family, designed specifically for applications demanding high-accuracy timekeeping, secure nonvolatile storage, and minimal external component count in space-constrained embedded systems.

FAQ

What is the maximum I²C clock frequency supported by the X1226S8ZT1?

The X1226S8ZT1 supports a maximum 2-wire™ interface speed of 400kHz, fully interoperable with standard I²C fast-mode timing. This allows rapid configuration of clock registers and EEPROM writes without bus arbitration delays. The SDA output uses slope-controlled pull-down to meet rise/fall time requirements at this speed, and the SCL input buffer remains always active for robust clock synchronization. No external speed-limiting resistors are required for compliance.

Does the X1226S8ZT1 require an external crystal, and what are the layout recommendations?

Yes, the X1226S8ZT1 requires an external 32.768kHz quartz crystal connected between X1 and X2 pins. Recommended part is Citizen CFS206-32.768KDZF. Layout must include a solid ground plane beneath the device, short symmetric traces (<5mm) to X1/X2, and no routing of noisy signals near the crystal path. The datasheet specifies that board and package parasitics add ~2pF to the on-die ATR-adjustable capacitance range (3.25–18.75pF), so total load should target 12.5pF for optimal stability.

How does the X1226S8ZT1 handle power failure and time recovery?

Upon total power loss (both VCC and VBACK = 0V), the X1226S8ZT1 sets the RTCF bit in the Status Register and holds all registers in default state. The clock will not increment until at least one byte is written to an RTC register - ensuring time validity before resumption. During partial failure (VCC drop only), VBACK sustains RTC operation and SRAM; the BAT bit indicates backup power active. Recovery requires no host reinitialization beyond clearing RTCF via a valid RTC register write.

Can both alarms on the X1226S8ZT1 operate simultaneously, and how is interrupt priority managed?

Yes, both Alarm 0 and Alarm 1 on the X1226S8ZT1 can trigger independently and simultaneously. Each has dedicated AL0/AL1 status bits in the Status Register and individual enable bits (AL0E/AL1E) in the INT register. There is no hardware priority - the host reads AL0 and AL1 flags to determine which (or both) occurred. When PHZ/IRQ is configured as interrupt output, it asserts active-low for any enabled alarm match; pulse duration is 10–40ms, and repeat mode (IM bit) enables periodic assertion.

What EEPROM protection modes does the X1226S8ZT1 support, and how are they configured?

The X1226S8ZT1 supports eight BlockLock™ protection modes controlled by BP2/BP1/BP0 bits in the BL register (address 0010h). These modes lock segments ranging from first 8 pages (0000h–03FFh) to full array (0000h–7FFFh). Protection is nonvolatile and persists across power cycles. To enable, write the desired BP code while WEL and RWEL bits are set; once locked, writes to protected addresses are ignored and generate no ACK. Unlocking requires clearing BP bits using the same write sequence.