CY7C63722C_11 Datasheet, PDF (10/53 Pages) Cypress Semiconductor – enCoRe USB Combination Low-Speed USB and PS/2 Peripheral Controller

CY7C63722C
CY7C63723C
CY7C63743C
Clocking
The chip can be clocked from either the internal on-chip clock, or from an oscillator based on an external resonator/crystal, as shown
in Figure . No additional capacitance is included on chip at the XTALIN/OUT pins. Operation is controlled by the Clock Configuration
Register, Figure .
Figure 3. Clock Oscillator On-chip Circuit
Int Clk Output Disable
Internal Osc
XTALOUT
Ext Clk Enable
Clk2x (12 MHz)
(to Microcontroller)
Clk1x (6 MHz)
(to USB SIE)
Clock
Doubler
Port 2.1
XTALIN
Figure 4. Clock Configuration Register (Address 0xF8)
Bit #
Bit Name
7
Ext. Clock
Resume
Delay
Read/Write
R/W
Reset
0
6
5
4
Wake-up Timer Adjust Bit [2:0]
R/W
R/W
R/W
0
0
0
3
Low-voltage
Reset
Disable
R/W
0
2
Precision
USB
Clocking
Enable
R/W
0
1
Internal
Clock
Output
Disable
R/W
0
0
External
Oscillator
Enable
R/W
0
Bit 7: Ext. Clock Resume Delay
External Clock Resume Delay bit selects the delay time when
switching to the external oscillator from the internal oscillator
mode, or when waking from suspend mode with the external
oscillator enabled.
1 = 4 ms delay.
0 = 128 s delay.
The delay gives the oscillator time to start up. The shorter time
is adequate for operation with ceramic resonators, while the
longer time is preferred for start-up with a crystal. (These
times do not include an initial oscillator start-up time which
depends on the resonating element. This time is typically
50–100 s for ceramic resonators and 1–10 ms for crystals).
Note that this bit only selects the delay time for the external
clock mode. When waking from suspend mode with the inter-
nal oscillator (Bit 0 is LOW), the delay time is only 8 s in
addition to a delay of approximately 1 s for the oscillator to
start.
Bit [6:4]: Wake-up Timer Adjust Bit [2:0]
The Wake-up Timer Adjust Bits are used to adjust the
Wake-up timer period.
If the Wake-up interrupt is enabled in the Global Interrupt En-
able Register, the microcontroller will generate wake-up inter-
rupts periodically. The frequency of these periodical wake-up
interrupts is adjusted by setting the Wake-up Timer Adjust Bit
[2:0], as described in Section . One common use of the
wake-up interrupts is to generate periodical wake-up events
during suspend mode to check for changes, such as looking
for movement in a mouse, while maintaining a low average
power.
Document #: 38-08022 Rev. *E
Page 10 of 53
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