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CY8C28xxx PSoC Programmable System-on-Chip TRM, Document No. 001-52594 Rev. *G
Digital Clocks
25.2.5
OSC_CR3 Register
The Oscillator Control Register 3 (OSC_CR3) selects the
divider value for variable clock 3 (VC3).
Bits 7 to 0: VC3 Divider[7:0].
As an example of the flexibil-
ity of the clocking structure in PSoC devices, consider a
device that is running off of an externally supplied clock at a
frequency of 93.7 kHz. This clock value may be divided by
the VC1 divider to achieve a VC1 clock net frequency of
5.89 kHz. The VC2 divider can reduce the frequency by
another factor of 16, resulting in a VC2 clock net frequency
of 366.02 Hz. Finally, the VC3 divider may choose VC2 as
its input clock and divide by 256, resulting in a VC3 clock net
frequency of 1.43 Hz.
The VC3 clock net can generate a system interrupt. After the
input clock and the divider value for the VC3 clock are cho-
sen, only one additional step is needed to enable the inter-
rupt; the VC3 mask bit must be set in register INT_MSK0[7].
When the VC3 mask bit is set, the VC3 clock generates
pending interrupts every number of clock periods equal to
the VC3 divider register value plus one. Therefore, if the
VC3 divider register’s value is 05h (divide by 6), an interrupt
occurs every six periods of the VC3’s input clock. Another
example is if the divider value was 00h (divide by one), an
interrupt is generated on every period of the VC3 clock. The
VC3 mask bit only controls the ability of a posted interrupt to
become pending. Because there is no enable for the VC3
interrupt, VC3 interrupts will always be posting. See the
Interrupt Controller chapter on page 65
for more information
on posting and pending.
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,DFh
VC3 Divider[7:0]
RW : 00
Table 25-3. OSC_CR3[7:0] Bits: VC3 Divider Value
Bits
Divider Source Clock
SYSCLKX2
SYSCLK
VC1
VC2
00h
SYSCLKX2
SYSCLK
VC1
VC2
01h
SYSCLKX2 / 2
SYSCLK / 2
VC1 / 2
VC2 / 2
02h
SYSCLKX2 / 3
SYSCLK / 3
VC1 / 3
VC2 / 3
03h
SYSCLKX2 / 4
SYSCLK / 4
VC1 / 4
VC2 / 4
...
...
...
...
...
FCh
SYSCLKX2 / 253
SYSCLK / 253
VC1 / 253
VC2 / 253
FDh
SYSCLKX2 / 254
SYSCLK / 254
VC1 / 254
VC2 / 254
FEh
SYSCLKX2 / 255
SYSCLK / 255
VC1 / 255
VC2 / 255
FFh
SYSCLKX2 / 256
SYSCLK / 256
VC1 / 256
VC2 / 256
Summary of Contents for CY8C28 series
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