CF2 API Reference (PDF) - Persistor Instruments Inc

CF2 API ReferenceReal Time Clock Drivers and FunctionsReal Time Clock OperationThe 68332 has no onboard Real Time Clock (RTC). The RTC function is provided by a Texas InstrumentsMSP430 microcontroller which lives on the CF2 board with the 68332. The MSP430 is clocked by a 40 KHzcrystal, and powered by either the main supply or an off-board backup battery. The RTC crystal is a tuningfork resonator with an initial accuracy of +/-20ppm with the parabolic temperature versus frequency curvetypical of these types of crystals. The MSP430 feeds this same signal to the 68332 PLL for system clockgeneration.Low-level software in the 68332 maintains communications with the MSP430. While the 68332 is on itmaintains its own internal clock which is synchronized with the MP430. When power is removed the MSP430maintains time and continues to run from the lithium battery (this assumes you are using a Recipe Card).When power is re-applied, the 68332 restarts and synchronizes its internal clock from the MSP430.Elapsed and Countdown TimersThe countdown and elapsed time functions provide convenient methods for measuring short intervals orwaiting for a timeout. These functions work with and return values normalized to microseconds. Time ismeasured with a fundamental unit of 40000 Hz.. Thus, the timer is internally counted as an integer numberof these ‘ticks’. One tick is approximately 25 µsecs and with a calling overhead for the functions that interactwith these counters of about 20 µsecs, the timers have an effective resolution of no less than 50 µsecs. Theelapsed and countdown timers have a maximum span of about 1.2 hours before overflowing. Below is anexample of usage:RTCTimer tmtest;...RTCElapsedTimerSetup(&tmtest);< code block being measured >printf("Elapsed time %ld us \n", RTCElapsedTime(&tmtest));RTCDelayMicroSeconds -- Delay for microsecondsDescription:Prototype:Inputs:Returns:Notes:Provides a simple means to kill a specific amount of time, specified in microseconds. Thisperforms much the same function as RTCDelayTicks but takes its argument in microseconds.The resolution of the calculation from microseconds to ticks which the real time clock canmeasure is about 25 µsecsbool RTCDelayMicroSeconds (ulong d);d is a ulong containing the number of microseconds to wait before returning.Returns a boolean that is TRUE unless the clock is stopped at the time RTCDelayMicroSecondsis called.RTCDelayMicroSeconds behavior in the event that the RTC is stopped is dependent on the actionspecified by RTCEnableErrTrap. Normally, it will simply return FALSE if the clock is stopped but iferror trapping is enabled by RTCEnableErrTrap then the machine will crash and print debuginformation. Because internally the real time clock can only measure time in units of ticks, thecountdown is counted in an integer number of ticks. Because one tick is approximately 25 µsecsand the calling overhead of the functions that interact with the clock is around 20 µsecs, delaysof less than 55 µsecs are meaningless and that RTCDelayMicroSeconds has an effectiveresolution of 55 µsecs.PERSISTORInstruments Inc.49 of 84CF2 API Reference7/19/2005