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Section 19 Keyboard Buffer Control Unit (PS2)
• Canceling software standby mode and watch mode
Software standby mode and watch mode are cancelled by a first KCLK falling interrupt. In this
case, an interrupt is generated at the first KCLK since software standby mode or watch mode
has been shifted (figure 19.17).
Notes on canceling operation are explained below.
When a transition to software standby mode or watch mode is performed while both
KBIOE and KCIE are set to 1, canceling the current mode is enabled by a first KCLK
falling interrupt (the KBE and KBTS are not affected).
When software standby mode and watch mode are cancelled by a first KCLK falling
interrupt, the KCIF flag is not set (only the internal flag is set).
In the first KCLK interrupt handling routine, the KCIF bit is checked. If the KCIF is 0, it
indicates that the interrupt is generated after software standby mode and watch mode have
been cancelled.
When software standby mode or watch mode is cancelled by receiving a receive clock, the
reception is ignored. Execute reception terminating processing by an interrupt handing
routine, and then request retransfer.
When transition to software standby mode or watch mode is made and the mode is
canceled by a first KCLK falling interrupt during data transmission, state before
performing mode transition is held immediately after canceling the mode. Therefore,
initialization by an interrupt handling routine is required. Precautions as (b) and (c) which
are shown in figure 19.17 should be applied on interrupt generation.
Priority of canceling software standby mode and watch mode is decided by the setting of
ICR.
The interrupt signal path and flag setting of the first KCLK interrupt in normal operation
differ from those in software standby mode and watch mode. Figure 19.6 shows the
interrupt signal paths of the first KCLK interrupt.
Signal A: Interrupt signal in normal operation
Signal B: Interrupt signal in software standby mode and watch mode
KCLK is input directly to the interrupt control block, not through the PS2, in software
standby mode and watch mode, and then an interrupt is generated by detection of a falling
edge. Therefore, the KCIF flag is not set. In this case, a flag that is in the interrupt control
block is set. The internal flag is automatically cleared after an interrupt request is sent to
the CPU. Figure 19.18 shows setting and clearing timing.
Rev. 1.00 May 09, 2008 Page 576 of 954
REJ09B0462-0100
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