PMU & PLL
7-4
GMS30C7201 Data Sheet
FCLK (ARM Processor and SDRAM controller clock)
Derived from PLL3 whose Frequency is controllable between 49.7664 MHz and 82.944
MHz. Frequency of operation is set using a 6 bit register.
There are two methods for updating frequency, depending upon the state of bit 6 of the
Clock Control register ClkCtl (see
ClkCtl register
on page 7-11). If bit 6 is set, then any
data written to bits [5:0] of the ClkCtl register are immediately transferred to the pins of
PLL3, thus causing the loop to unlock and to mute FCLK. This is only a safe mode of
operation if PLL3 frequency and mark-space ratio is guaranteed to be within limits
immediately after the Lock Detect signal has become active. If bit 6 is NOT set, then
the GMS30C7201 must enter DEEP sleep mode before bits [5:0] of the Clock Control
register are transferred to PLL3.
To switch between the two frequencies when bit 6 is not set:
Software writes the new value into the ClkCtl register
Set a Real Time Clock Alarm to wake the GMS30C7201 in 2 seconds
Enter DEEP SLEEP Mode by writing to the PMUMode Register
The GMS30C7201 will power up with PLL3 running at the new frequency
BCLK
BusClock, which is generated by the PMU by dividing FCLK by 2.
VCLK
Clock for the LCD and VGA video controller. Frequency selectable between 31.5MHz
or 40MHz. The VCLK PLL is disabled when on BnRES is active or when the PMU is
put into DEEP SLEEP mode. On exit from either of these conditions, the VCLK PLL
must be re-enabled by software.
Changing Frequency:
1
Software must first disable the VCLK pll, by writing a
‘
0
’
to the PLL1Enable bit
of the ClkCtl register.
2
Write the new value to the PLL1Freq bit.
3
Re-enable the VCLK pll by writing 1 to the PLL1Enable bit.
CCLK
Clock for the IR comms and the USB. Nominally 48MHz. The CCLK PLL is disabled
when BnRES active or when the PMU is put into DEEP SLEEP mode. On exit from
either of these conditions, the CCLK PLL must be re-enabled by software.
PMU state machine
The state machine handles the transition between the power management states
described below. The CPU can write to the PMU mode registers (which is what would
typically happen when a user switches off the device) and the state machine will
proceed to the commanded state.