4.3 ResetsThe graphics controller provides the following four reset sources:• external RESET• user reset via the control bit SYSRESET.PLLRESET• user reset via the control bit SYSRESET.SWRESET• system watchdog reset WDRESETThe different resets act on different targets:System reset A system reset is applied to all modules except the clock generator circuitry. Allregisters except SYSPLLCTRL and SYSCLKCTRL take on their default values.Consequently the clock generator circuitry is kept in operation and the mainsystem clock supply HCLK is maintained. That means in particular that thegraphics controller is ready to operate in very short time.All reset sources trigger a system reset.SYSCLKCTRL reset A reset of the SYSCLKCTRL register is initiated only by an external RESET.Since the external RESET initializes the entire graphics controller, it comes up withall default settings, partly defined by the MODE pins due to the boot modefunction.PLL reset The effect of a PLL reset differs depending on the reset source:• external RESETAn external RESET sets the SYSPLLCTRL register to its defaultvalues, defined by MODE[5:4], and restarts the PLL with the defaultparameters in SYSPLLCTRL.• by user SYSRESET.PLLRESET = 1This user reset restart only the PLL, but does not reset theSYSPLLCTRL register - and hence does not apply the MODE[5:4]default settings to the register.Purpose of this reset is to enable the user to set up own PLLparameters in SYSPLLCTRL and to restart the PLL with theseparameters.Note that this reset only changes the PLL parameters - and thereforeits output frequency -, but not the values of the main system clockdivider BUSDIV[1:0] and the Video Output clocks dividersVOnDIV[5:0] in the SYSCLKCTRL register.The table below informs about which reset source acts on which reset target.Table 4-1 Reset sources and targetsResetsourceSystemresetPLL reset SYSCLKCTRLreset PurposeSYSPLLCTRLresetPLLrestartRESET yes yes yes yescomplete reset with PLL/clocksetup configuration according toboot mode pinsSYSRESET.PLLRESET yes no yes nosoftware reconfiguration of PLLsettings (after write toSYSPLLCTRL)System Controller Chapter 4Preliminary User's Manual S19203EE1V3UM00 91
