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Chapter 9 Reset
8.Reset Operation Modes
8. Reset Operation Modes
The following two different modes can be used for an operation reset (RST):
• Normal (asynchronous) reset mode
• Synchronous reset mode
Which mode to use is specified by the synchronous reset operation enable bit (TBCR.SYNCR).
Pin input resets and watchdog resets always use normal reset mode.
For software resets, either normal reset mode or synchronous reset mode can be selected.
8.1 Normal (Asynchronous) Reset Mode
Normal reset operation refers to the mode when the device goes to the operation reset (RST) state
immediately after an operation reset (RST) request occurs.
For a normal reset, the device changes to the reset (RST) state immediately after a reset (RST)
request is received regardless of the current state of internal bus access.
In normal reset mode, the result on any bus operation that is in progress at the time the device
changes state is not guaranteed. However, acceptance of the operation reset (RST) request is
guaranteed.
Setting the synchronous reset operation enable bit (TBCR.SYNCR) to “0” specifies normal reset
mode.
Normal reset mode is the default setting after a settings initialization reset (INIT).
8.2 Synchronous Reset Operation
Synchronous reset operation refers to the mode when the device does not go to the operation reset
(RST) state after a operation reset (RST) request until after all bus access has halted.
In synchronous reset mode, the device does not go to the reset (RST) state when a reset (RST)
request is received if internal bus access is still in progress.
When such a reset request is received, a sleep request is issued to the internal bus. The device
does not change to the operation reset (RST) state until all buses have shutdown operation and
changed to sleep mode.
In synchronous reset mode, the results of bus operations are guaranteed because the device does
not change state until all bus access has halted.
However, if bus access should not halt for some reason, no requests can be received while bus
operation continues. In such a case, the settings initialization reset (INIT) remains available at any
time.
The following lists cases in which bus access may not stop:
If bus wait is enabled due to continuous input of RDY (ready request) to the external expansion bus
interface.