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8 Enabling the SSCG Unit
It is important to follow an specific scheme to enable the SSCG unit in order to avoid causing a spike
on the clock signal of the effected clock domains.
Note that the registers used in the following example description are in the CRG (Base Address:
FFFE_7000) and the SSCG (Base Address: FFFE_7080) units!
1. Switch the internal clock domains to the non-SSCG modulated clock domain, reset the SSCG
and switch the display clocks to the non-SSCG modulated clock domain:
CSEL <0xFFFE_7034> = 0x00000000
2. Set the SSCG to Bypass mode and power down the SSCG:
SSCG_CTRL <FFFE_70A0*> = 0x80010111
* FFFE_7080 + 20
3. Power up the SSCG and set to Bypass mode:
SSCG_CTRL <FFFE_70A0> = 0x00010111
4. Configure the SSCG and wait for 1000 clock cycles before starting the SSCG (Period 20 kHz)
SSCG_PERIOD <0xFFFE_7080> = 0x00000082
SSCG_PERIOD_JITTER <0xFFFE_7084> = 0x00000070
SSCG_FSTEP <0xFFFE_7088> = 0x000050A8
5. Disable the Bypass mode (enabling the SSCG unit):
SSCG_CTRL <0xFFFE_70A0> = 0x00000111
6. Switch the display clock domains to the SSCG modulated clock domain:
CSEL <0xFFFE_7034> = 0x00000004
7. Enable the SSCG:
SSCG_ENABLE <0xFFFE_70A4> = 0x00000001
8. Wait for 1 millisecond
9. Reset the 'Frequency Limit' Interrupt:
SSCG_IEN.IEn_Frequency_Limit <0xFFFE_70AC> = 0x00000001
10. Check that SSCG_STATUS.STS_FREQUENCY_LIMIT = 0
Note:
The SSCG parameter configuration can be done in steps 4 .. 7; otherwise the SSCG will run with the
default settings of <0xFFFE_7080> = content of address 0xFFFE_7080.
A more detailled flow is described in the Hardware Manual.
9 Checking the SSCG Unit is Operating
You can check that the SSCG unit is operating by reading the SSCG_CNTOUTFREQ register. It will
return a value that is not '0' if the SSCG is running.
10 Important Notes during operation
Note that not every receiver can handle a modulated output signal. If problems (screen artefacts etc.)
are experienced with a display, try reducing the degree of modulation to attain a range that the
receiver can accept.
Make sure that the SSCG configuration is a valid one (i.e. the constraints of the Hardware Manual are
taken into consideration). Failure to do this – i.e. an illegal configuration - may generate a flood of
interrupts from the SSCG unit.
Do not reconfigure the SSCG unit while it is being used!
Version 1.30
16
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