CY7C63722C Datasheet, PDF (13/53 Pages) Cypress Semiconductor – enCoRe™ USB Combination Low-Speed USB and PS/2 Peripheral Controller

CY7C63722C
CY7C63723C
CY7C63743C
Suspend Mode
Clocking Mode on Wake-up from Suspend
When exiting suspend on a wake-up event, the device can be
The CY7C637xxC parts support a versatile low-power suspend _{configured to run in either Internal or External Clock mode. The}
mode. In suspend mode, only an enabled interrupt or a LOW
mode is selected by the state of the External Oscillator Enable
state on the D–/SDATA pin will wake the part. Two options are
bit in the Clock Configuration Register (Figure ). Using the
available. For lowest power, all internal circuits can be disabled, _{Internal Clock saves the external oscillator start-up time and}
so only an external event will resume operation. Alternatively, a _{keeps that oscillator off for additional power savings. The}
low-power internal wake-up timer can be used to trigger the
wake-up interrupt. This timer is described in Section , and can be
used to periodically poll the system to check for changes, such
as looking for movement in a mouse, while maintaining a low
average power.
The CY7C637xxC is placed into a low-power state by setting the
Suspend bit of the Processor Status and Control Register
(Figure 33). All logic blocks in the device are turned off except
the GPIO interrupt logic, the D–/SDATA pin input receiver, and
(optionally) the wake-up timer. The clock oscillators, as well as
the free-running and Watchdog timers are shut down. Only the
external oscillator mode can be activated when desired, similar
to operation at power-up.
s _{The sequence of events for these modes is as follows:}
n _{Wake in Internal Clock Mode:}
ig ^{1. Before entering suspend, clear bit 0 of the Clock Configuration}
Register. This selects Internal clock mode after suspend.
s _{2. Enter suspend mode by setting the suspend bit of the}
e _{Processor Status and Control Register.}
D ^{3. After a wake-up event, the internal clock starts immediately}
occurrence of an enabled GPIO interrupt, wake-up interrupt, SPI
slave interrupt, or a LOW state on the D–/SDATA pin will wake
w _{the part from suspend (D– LOW indicates non-idle USB activity).}
e ^{Once one of these resuming conditions occurs, clocks will be}
restarted and the device returns to full operation after the oscil-
N ^{lator is stable and the selected delay period expires. This delay}
period is determined by selection of internal vs. external clock,
r _{and by the state of the Ext. Clock Resume Delay as explained in}
Section .
fo _{In suspend mode, any enabled and pending interrupt will wake}
the part up. The state of the Interrupt Enable Sense bit (Bit 2,
d Figure 33) does not have any effect. As a result, any interrupts
not intended for waking from suspend should be disabled
e _{through the Global Interrupt Enable Register and the USB End}
d Point Interrupt Enable Register (Section ).
n ^{If a resuming condition exists when the suspend bit is set, the}
part will still go into suspend and then awake after the appro-
e _{priate delay time. The Run bit in the Processor Status and}
Control Register must be set for the part to resume out of
m suspend.
Once the clock is stable and the delay time has expired, the
m _{microcontroller will execute the instruction following the I/O write}
that placed the device into suspend mode before servicing any
o _{interrupt requests.}
c _{To achieve the lowest possible current during suspend mode, all}
e _{I/O should be held at either VCC or ground. In addition, the GPIO}
bit interrupts (Figure 37 and Figure 38) should be disabled for
R _{any pins that are not being used for a wake-up interrupt. This}
should be done even if the main GPIO Interrupt Enable (Figure )
t _{is off.}
o _{Typical code for entering suspend is shown below:}
...
; All GPIO set to low-power state (no floating
N _{pins, and bit interrupts disabled unless using}
for wake-up)
(within 2 μs).
4. A time-out period of 8 μs passes, and then firmware execution
begins.
5. At some later point, to activate External Clock mode, set bit 0
of the Clock Configuration Register. This halts the internal
clocks while the external clock becomes stable. After an
additional time-out (128 μs or 4 ms, see Section ), firmware
execution resumes.
Wake in External Clock Mode:
1. Before entering suspend, the external clock must be selected
by setting bit 0 of the Clock Configuration Register. Make sure
this bit is still set when suspend mode is entered. This selects
External clock mode after suspend.
2. Enter suspend mode by setting the suspend bit of the
Processor Status and Control Register.
3. After a wake-up event, the external oscillator is started. The
clock is monitored for stability (this takes approximately
50–100 μs with a ceramic resonator).
4. After an additional time-out period (128 μs or 4 ms, see
Section ), firmware execution resumes.
Wake-up Timer
The wake-up timer runs whenever the wake-up interrupt is
enabled, and is turned off whenever that interrupt is disabled.
Operation is independent of whether the device is in suspend
mode or if the global interrupt bit is enabled. Only the Wake-up
Timer Interrupt Enable bit (Figure ) controls the wake-up timer.
Once this timer is activated, it will give interrupts after its time-out
period (see below). These interrupts continue periodically until
the interrupt is disabled. Whenever the interrupt is disabled, the
wake-up timer is reset, so that a subsequent enable always
results in a full wake-up time.
...
; Enable GPIO and/or wake-up timer ^{The wake-up timer can be adjusted by the user through the}
interrupts if desired for wake-up
Wake-up Timer Adjust bits in the Clock Configuration Register
...
; Select clock mode for wake-up (see Section ) ^{(Figure ). These bits clear on reset. In addition to allowing the}
mov a, 09h ; Set suspend and run bits
user to select a range for the wake-up time, a firmware algorithm
iowr FFh
; Write to Status and Control Register – Enter ^{can be used to tune out initial process and operating condition}
suspend, wait for GPIO/wake-up interrupt or ^{variations in this wake-up time. This can be done by timing the}
USB activity
wake-up interrupt time with the accurate 1.024-ms timer
nop
; This executes before any ISR
interrupt, and adjusting the Timer Adjust bits accordingly to
...
; Remaining code for exiting suspend routine ^{approximate the desired wake-up time.}
Document #: 38-08022 Rev. *D
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