24 MHz fundamental-mode crystal: what the specs govern
The ECS-240-18-5PLX-AGN-TR: The 24 MHz fundamental-mode HC-49/US crystal from ECS Inc. is the part that sets the microcontroller's clock tick rate — the PLL multiplies this reference up to the core and peripheral clocks, so any frequency error in the crystal propagates directly into baud-rate generation and cycle-counting delays. With 30Ω ESR the oscillator startup circuit sees minimal series resistance, which matters in low-power MCU designs that drive the crystal hard only during the initial startup burst. Load capacitance is 18pF, which the MCU's on-chip load caps must complement to hit the target 24 MHz within the ±30ppm stability band — a common mistake is leaving the oscillator trim code at factory default when the board-level capacitance budget differs from the datasheet test condition. At 11.40 mm × 4.80 mm with a 3.20 mm seated height, the HC-49/US package is a through-hole-style crystal adapted for surface-mount reflow — the Gull Wing leads demand a compatible pad stack and the body sits above the board enough to avoid tombstoning on heavy paste deposits. The 30Ω ESR figure is specified at the fundamental frequency; at higher temperatures ESR rises and startup margin narrows, which is why the oscillator design guidelines for most Cortex-M MCUs include a startup-time budget that assumes worst-case ESR at temperature. Packaged on tape and reel per, the CSM-7X series is a standard commercial reel size — reel quantities are typically 1,000 pieces per reel, which is the BOM planning quantity to match against reel packaging for pick-and-place line setup. The ±25ppm frequency tolerance at 25°C is the initial production tolerance; the ±30ppm stability budget then absorbs the drift across the operating temperature range, giving a combined ±55ppm worst-case swing from a cold 25°C room measurement to a hot operating condition.
Active status and sourcing reality
ECS Inc. lists this part as Active per — it is a current-production line with no stated NRND or EOL notice in the ledger.