User`s guide

CY7C63722C
CY7C63723C
CY7C63743C
FOR
FOR
Document #: 38-08022 Rev. *C Page 10 of 49
9.0 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 9-1. No additional capacitance is included on
chip at the XTALIN/OUT pins. Operation is controlled by the
Clock Configuration Register, Figure 9-2.
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 µs 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 µs 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 internal oscillator (Bit 0 is LOW), the delay time is
only 8 µs in addition to a delay of approximately 1 µs 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
Enable Register, the microcontroller will generate wake-up
interrupts periodically. The frequency of these periodical
wake-up interrupts is adjusted by setting the Wake-up Tim-
er Adjust Bit [2:0], as described in Section 11.2. One com-
mon use of the wake-up interrupts is to generate periodical
wake-up events during suspend mode to check for chang-
es, such as looking for movement in a mouse, while main-
taining a low average power.
Bit 3: Low-voltage Reset Disable
When V
CC
drops below V
LVR
(see Section 25.0 for the val-
ue of V
LVR
) and the Low-voltage Reset circuit is enabled,
the microcontroller enters a partial suspend state for a pe-
riod of t
START
(see Section 26.0 for the value of t
START
).
Program execution begins from address 0x0000 after this
t
START
delay period. This provides time for V
CC
to stabilize
Figure 9-1. Clock Oscillator On-chip Circuit
XTALOUT
XTALIN
Clk2x (12 MHz)
Clock
Doubler
Clk1x (6 MHz)
(to Microcontroller)
(to USB SIE)
Port 2.1
Internal Osc
Int Clk Output Disable
Ext Clk Enable
Bit # 76543210
Bit Name Ext. Clock
Resume
Delay
Wake-up Timer Adjust Bit [2:0] Low-voltage
Reset
Disable
Precision
USB
Clocking
Enable
Internal
Clock
Output
Disable
External
Oscillator
Enable
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Reset 00000000
Figure 9-2. Clock Configuration Register (Address 0xF8)