Renesas CDP68HC68T1M296

Overview

CDP68HC68T1M296 from Intersil is a CMOS serial real-time clock IC with integrated 32×8-bit static RAM, SPI interface, power-sense/control logic, and programmable buffered clock output. It provides BCD-formatted time/calendar (seconds to years), 12/24-hour mode with AM/PM flag, alarm, periodic interrupts, and watchdog reset capability. Used in embedded systems requiring battery-backed timekeeping and intelligent power management.

For engineers reviewing the CDP68HC68T1M296 datasheet, CDP68HC68T1M296 pinout, CDP68HC68T1M296 application, or CDP68HC68T1M296 equivalent, key selection criteria include its 3-wire SPI interface, dual-clock source support (32kHz crystal or 50/60Hz line input), 2.2V minimum standby voltage, three independent interrupt modes (alarm/periodic/power-fail), and CPUR open-drain reset output for processor supervision.

Technical Context

The CDP68HC68T1M296 implements a prescaler-driven 1Hz timebase derived either from an internal oscillator (with 32kHz, 1MHz, 2MHz, or 4MHz crystal) or external 50/60Hz AC line input via the LINE pin. Its clock/calendar registers (addresses $20–$26) and alarm latches ($28–$2A) operate in BCD format and support automatic leap-year correction.

Power control is managed through VSYS/VBATT interaction: VSYS level at end of POR selects single-supply or battery-backup mode; PSE output enables system power rail control; CPUR delivers open-drain reset pulses; and INT provides wired-OR interrupt signaling with status-latched cause (power fail/alarm/periodic). The watchdog requires CE pin toggling without serial transfer to prevent CPU reset.

Key Specifications

Pinout & Package

CDP68HC68T1M296 is packaged in a 16-lead SOIC (Small Outline Integrated Circuit) with Pb-free RoHS-compliant finish (package drawing M16.3), optimized for surface-mount reflow assembly.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar real-time clock with RAM and power management applications.

Compared with DS1307+ and PCF8563, the CDP68HC68T1M296 uniquely integrates SPI, AC line input, power-sense logic, CPUR reset, and PSE rail control in one package - enabling complete autonomous power management without external supervisors or glue logic.

Availability

CDP68HC68T1M296 is available at Aetrix Electronics and suitable for industrial HMI panels, energy metering systems, medical infusion pumps, and point-of-sale terminals requiring stable component supply with long-term lifecycle support.

Supply support for CDP68HC68T1M296 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 manufacturer specializing in precision analog, power management, and timing solutions for industrial, automotive, and communications markets.

The CDP68HC68T1 product line was designed for embedded systems needing integrated RTC, nonvolatile RAM, and intelligent power supervision - targeting applications where battery backup, power-fail response, and processor reset coordination are critical.

FAQ

What clock sources does the CDP68HC68T1M296 support?

The CDP68HC68T1M296 supports four crystal frequencies (32.768kHz, 1.048576MHz, 2.097152MHz, 4.194304MHz) selected via the Clock Control Register, or an external 50Hz/60Hz AC signal applied to the LINE pin. Crystal operation is mandatory when power-sense mode is enabled, as the LINE input is disconnected from the prescaler in that configuration. The CDP68HC68T1M296 does not support arbitrary clock frequencies outside these defined options.

How does the CDP68HC68T1M296 handle power failure detection?

The CDP68HC68T1M296 detects power failure using two complementary methods: (1) VSYS/VBATT comparison - when VSYS drops below VBATT +1.0V, the device enters battery-backup mode and asserts PSE low; (2) LINE pin monitoring - with Bit 5 set in the Interrupt Control Register, AC zero-crossing loss on the LINE pin triggers a power-fail interrupt after 2.68–4.64ms delay. Both mechanisms set the Power-sense Interrupt bit in the Status Register and drive INT low. The CDP68HC68T1M296 requires crystal operation for method (2).

Can the CDP68HC68T1M296 operate with only a battery supply?

Yes, the CDP68HC68T1M296 supports true battery-backup operation. When VSYS is low at end-of-POR, it enters battery-backup mode: CLKOUT, CPUR, and PSE are held low until VSYS rises ~1.0V above VBATT. During this state, the oscillator runs from VBATT, timekeeping continues at 2.2–6.0V, and RAM retains data. VDD may be unpowered. The CDP68HC68T1M296 maintains full RTC functionality including alarm and periodic interrupts while drawing only 10–500µA (depending on crystal frequency), making it suitable for multi-year battery operation.

What is the function of the CE pin beyond chip enable?

Beyond enabling the SPI interface, the CE pin serves as the watchdog trigger input. When Bit 7 (Watchdog) is set in the Interrupt Control Register, the CDP68HC68T1M296 requires the host CPU to toggle CE high/low periodically without initiating a serial transfer. Failure to do so within the timeout window causes the CDP68HC68T1M296 to assert CPUR low and set Bit 6 in the Status Register. This provides hardware-enforced CPU supervision independent of SPI traffic - a feature not found in most competing RTCs like DS1307+ or PCF8563.

Does the CDP68HC68T1M296 support both 12-hour and 24-hour time formats?

Yes, the CDP68HC68T1M296 supports both formats. Bit 7 of the Hours register ($22) selects mode: '1' enables 12-hour format with AM/PM indication in Bit 5; '0' selects 24-hour format (00–23). In 12-hour mode, hours are encoded as 01–12 (AM) or 21–32 (PM) in BCD; in 24-hour mode, values are 00–23. The CDP68HC68T1M296 automatically handles rollover and leap-year correction regardless of format, and the selection persists across power cycles when stored in the clock registers.