Watch Mode - Fujitsu F2MC-8FX Hardware Manual

6.8.5

Watch Mode

Watch mode allows only the subclock and watch prescaler to work. The operating clock
for the CPU and peripheral resources is stopped in this mode.
Operations in Watch Mode
In watch mode, the operating clock for the CPU and peripheral resources is stopped. The device stops all
the functions except the watch prescaler, watch counter, external interrupt, and low-voltage detection reset
while retaining the contents of registers and RAM that exist immediately before the transition to watch
mode.
Transition to watch mode
Writing "1" to the watch bit in the standby control register (STBC:TMD) causes the device to enter watch
mode if the system clock monitor bits in the system clock control register (SYCC: SCM1, 0) are "00".
The device can enter watch mode only when the clock mode is subclock mode. Upon transition to watch
mode, the states of external pins are retained when the pin state setting bit in the standby control register
(STBC:SPL) is "0", and the states of external pins become high impedance when that bit is "1" (those pins
are pulled up for which pull-up resistor connection has been selected in the pull-up setting register).
Cancellation of watch mode
The device is released from watch mode in response to a reset, watch interrupt, or external interrupt.
Note:
When watch mode is canceled via an interrupt, peripheral resources placed into watch mode during an action
resume that action. Therefore, the initial interval time of the interval timer and other similar settings are
rendered indeterminate. After recovery from watch mode, initialize each peripheral resource as necessary.
CHAPTER 6 CLOCK CONTROLLER
75