CY8C28xxx PSoC Programmable System-on-Chip TRM, Document No. 001-52594 Rev. *G
471
Digital Clocks
25.2.4
OSC_CR4 Register
The Oscillator Control Register 4 (OSC_CR4) selects the
input clock to variable clock 3 (VC3).
Bits 1 and 0: VC3 Input Select [1:0].
The VC3 clock net is
the only clock net with the ability to generate an interrupt.
The input clock of VC3 comes from a configurable source.
As shown in
, a 4-to-1 mux deter-
mines the clock that is used in the input to the VC3 divider.
The mux allows either the 48 MHz, 24 MHz, VC1, or VC2
clocks to be used as the input clock to the divider. Because
the selection of a clock for the VC3 divider is performed by a
simple 4-to-1 mux,
and glitches may be injected
to the VC3 divider when the OSC_CR4[1:0] bits are
changed. Care should be taken to ensure that blocks using
the VC3 clock are either disabled when OSC_CR4[1:0] is
changed or not sensitive to glitches. Unlike the VC1 and
VC2 clock dividers, the VC3 clock divider is 8-bits wide.
Therefore, there are 256 valid divider values as indicated by
It is important to remember that even though the VC3 divider
has four choices for the input clock, none of the choices
have fixed frequencies for all device configurations. Both the
24 MHz and 48 MHz clocks may have very different fre-
quencies if an external clock is in use. Also, the divider val-
ues for the VC1 and VC2 inputs to the mux must be
considered.
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,DEh
VC3 Input Select[1:0]
RW : 00
Table 25-2. OSC_CR4[1:0] Bits: VC3
Bits
Multiplexer Output
00b
SYSCLK
01b
VC1
10b
VC2
11b
SYSCLKX2
Содержание CY8C28 series
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Страница 93: ...92 CY8C28xxx PSoC Programmable System on Chip TRM Document No 001 52594 Rev G External Crystal Oscillator ECO ...
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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 ...
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