CY8C28xxx PSoC Programmable System-on-Chip TRM, Document No. 001-52594 Rev. *G
103
Sleep and Watchdog
12.3.6
OSC_CR2 Register
The Oscillator Control Register 2 (OSC_CR2) is used to
configure various features of internal clock sources and
clock nets.
Bit 7: PLLGAIN.
This is the only bit in the OSC_CR2 regis-
ter that directly influences the PLL. When set, this bit keeps
the PLL in a Low Gain mode. If this bit is held low, the lock
time is less than 10 ms. If this bit is held high, the lock time
is on the order of 50 ms. After lock is achieved, it is recom-
mended that this bit be forced high to decrease the jitter on
the output. If longer lock time is tolerable, the PLLGAIN bit
can be held high all the time.
Bit 4: SLP_EXTEND.
This bit allows for extended sleep
intervals, up to 16s.
Bit 3: WDR32_SE.
If an external 32 kHz crystal is used,
this bit allows a choice between the ECO or the ILO as the
source of the watchdog timer and sleep timer
Bit 2: EXTCLKEN.
When the EXTCLKEN bit is set, the
external clock becomes the source for the internal clock
tree, SYSCLK, which drives most PSoC device clocking
functions. All external and internal signals, including the 32
kHz clock, whether derived from the internal low speed
oscillator (ILO) or the crystal oscillator, are synchronized to
this clock source. If an external clock is enabled, PLL mode
should be off. The external clock input is located on port
P1[4]. When using this input, the pin drive mode should be
set to High-Z (not High-Z analog).
Bit 1: RSVD.
Reserved bit - This bit should always be 0.
Bit 0: SYSCLKX2DIS.
When set, the Internal Main Oscilla-
tor’s doubler is disabled. This results in a reduction of overall
device power, on the order of 1 mA. It is advised that any
application that does not require this doubled clock should
have it turned off.
For additional information, refer to the
12.3.7
ILO_TR Register
The Internal Low Speed Oscillator Trim Register (ILO_TR)
sets the adjustment for the internal low speed oscillator.
The device specific value, placed in the trim bits of this reg-
ister at boot time, is based on factory testing.
It is strongly
recommended that the user not alter the register value
.
Bits 5 and 4: Bias Trim[1:0].
These two bits are used to
set the bias current in the PTAT Current Source. Bit 5 gets
inverted, so that a medium bias is selected when both bits
are ‘0’. The bias current is set according to
Bits 3 to 0: Freq Trim[3:0].
These four bits are used to
trim the frequency. Bit 0 is the LSb and bit 3 is the MSb. Bit 3
gets inverted inside the register.
For additional information, refer to the
Address
Name
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
Access
1,E2h
PLLGAIN
SLP_EXTE
ND
WDR32_SE
EXTCLKEN
RSVD
SYSCLKX2
DIS
RW : 00
Address
Name
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
Access
1,E9h
Bias Trim[1:0]
Freq Trim[3:0]
RW : 00
Table 12-3. Bias Current in PTAT
Bias Current
Bias Trim [1:0]
Medium Bias
00b
Maximum Bias
01b
Minimum Bias
10b
Not needed *
11b
* About 15% higher than the minimum bias.
Summary of Contents for CY8C28 series
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