Clock/Calendar/Alarm with ATtiny12

Posted on Oct 8, 2012

This is the timekeeping test circuit. It includes a one-transistor circuit to switch in the 5V power supply when present and drop back to the 3v battery the rest of the time. That loop of blue wire-wrapping wire is a lariat used to quickly and easily pull the chip out of the socket during development without damage and without having to reach for the removal tool. Low current operation (chip sleeps most of the time). Alarm and external event triggered interpreter operation. Capable of stand-alone timer and alarm use. No additional processor required once programmed. One external input pin and one open drain output pin for interpreter.

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After programming, you must: 1. Select the Low Frequency Crystal oscillator 67ms + 32k clock, and 2. Disable Reset to free up pin 1 as open drain output. A DS interface allows access to a register file, EEPROM, and an instruction interpreter. A separate interpreter interprets instructions stored in the EEPROM. EEPROM interpreter operation can be initiated by a clock/calendar alarm, an external event, or by command via the DS interface. The register set plays a central role in moving information between the DS interface and the clock and EEPROM interpreter. One external input can be sampled by the interpreter and one external open drain output can be driven by the interpreter The clock's output can be read from registers 3 through 8, but writing to these registers does not affect the clock unless the "write time buffers to clock" flag is set in the control register (register $0F). See the Register Assignments section for more detail. It should be noted that this application of the DS Inteface has a time-out period of 1 to 2 seconds for both send and receive. This prevents the inteface from hanging up in applicatoins in which the DS Interface pins are exposed to shorts on in which DS Interface transactions are interrupted. It also puts contstraints on the response time of the host. As an example, to read the control register, the read comamnd ($1F) must be sent, and the host must respond to the clock's signal for...

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