CY8C28xxx PSoC Programmable System-on-Chip TRM, Document No. 001-52594 Rev. *G
473
Digital Clocks
25.2.6
OSC_CR0 Register
The Oscillator Control Register 0 (OSC_CR0) is used to
configure various features of internal clock sources and
clock nets.
Bit 7: 32k Select.
By default, the 32 kHz clock source is
the Internal Low-Speed Oscillator (ILO). Optionally, the
32.768 kHz External Crystal Oscillator (ECO) may be
selected.
Bit 6: PLL Mode.
This bit is the only bit that directly influ-
ences the PLL. When set, it enables the PLL. The EXTCLK
bit should be set low during PLL operation.
Bit 5: No Buzz.
Normally, when the Sleep bit is set in the
CPU_SCR register, all PSoC device systems are powered
down, including the bandgap reference. However, to facili-
tate the detection of POR and LVD events at a rate higher
than the sleep interval, the bandgap circuit is powered up
periodically (for about 60
s) at the Sleep System Duty
Cycle (set in ECO_TR), which is independent of the sleep
interval and typically higher. When the No Buzz bit is set, the
Sleep System Duty Cycle value is overridden and the band-
gap circuit is forced to be on during sleep. This results in
faster response to an LVD or POR event (continuous detec-
tion as opposed to periodic), at the expense of slightly
higher average sleep current.
Bits 4 and 3: Sleep[1:0].
The available sleep interval
selections are shown in
. Remember that when
the ILO is the selected 32 kHz clock source, sleep intervals
are approximate.
Bits 2 to 0: CPU Speed[2:0].
The PSoC M8C may operate
over a range of CPU clock speeds (
), allowing the
M8C’s performance and power requirements to be tailored
to the application.
The reset value for the CPU speed bits is zero. Therefore,
the default CPU speed is one-eighth of the clock source.
The internal main oscillator is the default clock source for
the CPU speed circuit; therefore, the default CPU speed is 3
MHz. See
for more informa-
tion on the supported frequencies for externally supplied
clocks.
The CPU frequency is changed with a write to the
OSC_CR0 register. There are eight frequencies generated
from a power-of-two divide circuit, which are selected by a
3-bit code. At any given time, the CPU 8-to-1 clock mux is
selecting one of the available frequencies, which is resyn-
chronized to the 24 MHz master clock at the output.
Regardless of the CPU speed bit’s setting, if the actual CPU
speed is greater than 12 MHz, the 24 MHz operating
requirements apply. An example of this scenario is a device
that is configured to use an external clock, which is supply-
ing a frequency of 20 MHz. If the CPU speed register’s
value is 0x03, the CPU clock is 20 MHz. Therefore, the sup-
ply voltage requirements for the device are the same as if
the part was operating at 24 MHz off of the internal main
oscillator. The operating voltage requirements are not
relaxed until the CPU speed is at 12.0 MHz or less.
Some devices support the slow IMO option, as discussed in
the IMO chapter in the
“Architectural Description” on
. This offers an option to lower both system and
CPU clock speed to save power.
An automatic protection mechanism is available for systems
that need to run at peak CPU clock speed but cannot guar-
antee a high enough supply voltage for that clock speed.
See the LVDTBEN bit in the
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,E0h
32k Select
PLL Mode
No Buzz
Sleep[1:0]
CPU Speed[2:0]
RW : 00
Table 25-4. Sleep Interval Selections
OSC_CR2[4]
Sleep Interval
OSC_CR0[4:3]
Sleep
Timer
Clocks
Sleep
Period
(nominal)
Watchdog
Period
(nominal)
0
00b (default)
64
1.95 ms
6 ms
0
01b
512
15.6 ms
47 ms
0
10b
4,096
125 ms
375 ms
0
11b
32,768
1 sec
3 sec
1
00b (default)
65,536
2 sec
6 sec
1
01b
131,072
4 sec
12 sec
1
10b
262,144
8 sec
24 sec
1
11b
524,288
16 sec
48 sec
Table 25-5. OSC_CR0[2:0] Bits: CPU Speed
Bits
6 MHz Internal
Main Oscillator *
24 MHz Internal
Main Oscillator
External Clock
000b
750 kHz
3 MHz
EXTCLK/ 8
001b
1.5 MHz
6 MHz
EXTCLK/ 4
010b
3 MHz
12 MHz
EXTCLK/ 2
011b
6 MHz
24 MHz
EXTCLK/ 1
100b
375 kHz
1.5 MHz
EXTCLK/ 16
101b
187.5 kHz
750 kHz
EXTCLK/ 32
110b
93.7 kHz
187.5 kHz
EXTCLK/ 128
111b
23.4 kHz
93.7 kHz
EXTCLK/ 256
* For PSoC devices that support the slow IMO option, see the
.
Содержание CY8C28 series
Страница 65: ...64 CY8C28xxx PSoC Programmable System on Chip TRM Document No 001 52594 Rev G RAM Paging ...
Страница 85: ...84 CY8C28xxx PSoC Programmable System on Chip TRM Document No 001 52594 Rev G Internal Main Oscillator IMO ...
Страница 93: ...92 CY8C28xxx PSoC Programmable System on Chip TRM Document No 001 52594 Rev G External Crystal Oscillator ECO ...
Страница 97: ...96 CY8C28xxx PSoC Programmable System on Chip TRM Document No 001 52594 Rev G Phase Locked Loop PLL ...
Страница 125: ...124 CY8C28xxx PSoC Programmable System on Chip TRM Document No 001 52594 Rev G ...
Страница 311: ...310 CY8C28xxx PSoC Programmable System on Chip TRM Document No 001 52594 Rev G IDAC_CR0 1 FDh ...
Страница 317: ...316 CY8C28xxx PSoC Programmable System on Chip TRM Document No 001 52594 Rev G ...
Страница 393: ...392 CY8C28xxx PSoC Programmable System on Chip TRM Document No 001 52594 Rev G ...
Страница 425: ...424 CY8C28xxx PSoC Programmable System on Chip TRM Document No 001 52594 Rev G Analog Reference ...
Страница 461: ...460 CY8C28xxx PSoC Programmable System on Chip TRM Document No 001 52594 Rev G Two Column Limited Analog System ...
Страница 477: ...476 CY8C28xxx PSoC Programmable System on Chip TRM Document No 001 52594 Rev G Digital Clocks ...
Страница 483: ...482 CY8C28xxx PSoC Programmable System on Chip TRM Document No 001 52594 Rev G Multiply Accumulate MAC ...
Страница 513: ...512 CY8C28xxx PSoC Programmable System on Chip TRM Document No 001 52594 Rev G Internal Voltage Reference ...
Страница 523: ...522 CY8C28xxx PSoC Programmable System on Chip TRM Document No 001 52594 Rev G Switch Mode Pump SMP ...
Страница 533: ...532 CY8C28xxx PSoC Programmable System on Chip TRM Document No 001 52594 Rev G I O Analog Multiplexer ...
Страница 537: ...536 CY8C28xxx PSoC Programmable System on Chip TRM Document No 001 52594 Rev G Real Time Clock RTC ...
Страница 561: ...560 CY8C28xxx PSoC Programmable System on Chip TRM Document No 001 52594 Rev G ...