Page 49 of 346 Start Back Next End ZBasic System Library 37 ZBasic Microcontrollers Section 3 - Processor Speed and Device Configuration Issues For ZX devices, the processor speed and configuration are fixed and specific to each device. The clock speed for most ATmega-based ZX devices is 14.7456MHz but special versions are available that run slower and faster. ZX devices based on the ATxmega run at 29.4912MHz. The table below summarizes the differences that arise due to the difference in operating speeds. ZX Device Processor Speed Variations Parameter 7.3728MHz 14.7456MHz 18.432MHz 29.4912MHz RTC Tick Frequency 512 Hz 512 Hz 500 Hz 512 Hz RTC Fast Tick Frequency 512 Hz 1024 Hz 1000 Hz 1024 Hz RTC Scale Factor 1 2 2 1 RTC Timer Frequency 115.2 KHz 230.4 KHz 72 KHz 115.2 KHz Multi-tasking Time Slice 1.95 mS 1.95 mS 2.0 mS 1.95 mS Default TimerSpeed1 Units 135.6 nS 67.8 nS 54.4 nS 67.8 nS Default TimerSpeed2 Units 1.085 µS 1.085 µS* 434 nS 271 nS CountTransitions() Sample Rate 204.8 KHz 409.6 KHz 512 KHz 737.3 KHz Note, particularly, that the “units” value for TimerSpeed2 on ZX devices running at 14.7456MHz is scaled to match the value corresponding to operating at 7.3728MHz. This is done for compatibility with BasicX devices that all operate at the lower speed. Consult the section I/O Timer Prescaler Values for information on which routines use the TimerSpeed1 and TimerSpeed2 values. The scaling effect described above can be disabled by setting the value of Register.IOScaling to False. For generic target devices, the processor speed can be any reasonable value and the RTC frequency can be any value attainable using the available prescaler and compare value settings for the RTC timer. Further, the initial I/O Timer prescaler settings Register.TimerSpeed1 and Register.TimerSpeed2 can be any useful values. Consquently, the meaning of results returned by some ZBasic System Library routines can only be described in terms of the value of these configurable items (all of which are specified at compile time). The table below gives several important values that are dependent on device configuration parameter values both in the case of ZX devices (with fixed values) or generic target devices (with user-specified values). The symbols given in the table entries is used in the descriptions of various ZBasic System Library routines thus allowing you to infer the meaning of the results based on device configuration values. ZBasic Device Parameters Device Parameter Symbol Example Value for ZX-24n Main Clock Frequency F_CPU 14.7456 MHz RTC Scale Factor RTC_SCALE 2 RTC Fast Tick Frequency F_RTC_FAST 1024 Hz RTC Tick Frequency F_RTC_TICK 512 Hz RTC Timer Frequency F_RTC_TIMER 230.4 KHz TimerSpeed1 Frequency F_TS1 14.7456 MHz¹ TimerSpeed2 Frequency F_TS2 1.8432 MHz² 1) Assuming the default Register.TimerSpeed1 value of 1. 2) Assuming the default Register.TimerSpeed2 value of 2. Main Clock Frequency (F_CPU) This value represents the operating speed of the target CPU. In the case of generic target devices, it is specified via the target device parameter ClockFrequency.