In some embodiments, a wearable physiologic monitor comprises an application-specific integrated circuit (ASIC) including signal conditioning circuitry, a real-time clock, digital control logic, and mode-selection logic for setting an operating mode of the ASIC to a stand-alone mode or a peripheral mode. In the stand-alone mode, the digital control logic periodically stores data packets including multiple sensor data types in a digital memory such as a removable flash memory card. In the peripheral mode, the data packets are transmitted to a microcontroller for processing. The monitor includes sensors such as electrocardiogram (ECG) electrodes, accelerometers, and a temperature sensor, some of which may be integrated on the ASIC. The same basic chip design may be used in the stand-alone mode in disposable patches, and in the peripheral mode in bedside devices. The operating mode may be chosen at monitor manufacture, by connecting input pins to mode-selection logic levels.