Frequency generator

Frequency generator is vital to CPU unit functioning, as well as programmable blocks. Each of programmable components has certain demands regarding speed. PSoC microcontrollers have a system for generation of different frequency signals, which is done by graphically selecting appropriate parameters. Picture shows two independent systems for generating signals SYSCLK and CLK 32k.

SYSCLK is the main internal clock signal with a speed of 24MHz. It is used as a reference clock for most of other signals.

SYSCLKx2 is a clock signal with double frequency (48MHz) of SYSCLK signal.

24V1 is a signal derived by dividing frequency SYSCLK with parameter N1, which varies in range from 1 to 16. 24V1 frequency equals SYSCLK/N1, with a frequency from 1.5MHz (N1=16) to 24MHz (N1=1).

24V2 is a signal derived by dividing 24MHz frequency with parameter N1, which varies in range between 1vand 16. 24V2 signal frequency equals SYSCLK/N1N2., which means that possible frequency ranges from

93.75kHz (N1,N2=16) to 24MHz (N1,N2=1).

24V3 signal is derived by dividing frequency of one of the signals 24V2, 24V1, SYSCLK or SYSCLKx2, with number N, in the range from 1 to 256.

CPU_CLK is used as a CPU unit frequency which has a direct impact on instruction execution speed.

CPU_CLK can have any of eight frequencies that are in range from 93.75MHz to 24MHz.

Frequency 24V1, 24V2, 24V3 and CPUCLK selection is done easily, by setting appropriate parameters in Device Editor or during program runtime by selecting three lower bits of OSCCR0 register.

CLK32K is a slow signal with a frequency of 32kHz. It can be used as a programmable component input. It can also be used for Sleep timer wake-up operation in the case when other SYSCLK derived signals are inactive.

Signal SYSCLK can be acquired using internal main oscillator (IMO), while CLK32K signal is acquired through internal local oscillator (ILO). Fault tolerance of 2.5% in the case of internal frequency generation, is the limit factor in a precise timing applications. In such case external SYSCLK clock reference should be used. External frequency ranges from 1 to 24MHz. It connects to PSoC through pin P1[4].

Similar situation is in the case of CLK32K, which also can be generated by internal local oscillator (ILO), as said before, or more precise external 32kHz oscillator. In the both cases microcontroller starts with internal

frequency generators, after which is necessary to satisfy appropriate procedure.