Datasheet

RL78/L12 CHAPTER 12 SERIAL ARRAY UNIT
R01UH0330EJ0200 Rev.2.00 494
Dec 13, 2013
12.6.3 SNOOZE mode function
The SNOOZE mode makes the UART perform reception operations upon RxDq pin input detection while in the STOP
mode. Normally the UART stops communication in the STOP mode. However, using the SNOOZE mode enables the
UART to perform reception operations without CPU operation upon detection of the RxDq pin input.
Only the following channel can be set to the SNOOZE mode.
UART0
When using UARTq in the SNOOZE mode, make the following settings before entering the STOP mode. (See Figure
12-90 Flowchart of SNOOZE Mode Operation (EOCm1 = 0, SSECm = 0/1 or EOCm1 = 1, SSECm = 0) and Figure 12-
92 Flowchart of SNOOZE Mode Operation (EOCm1 = 1, SSECm = 1).)
• In the SNOOZE mode, the baud rate setting for UART reception needs to be changed to a value different from that
in normal operation. Set the SPSm register and bits 15 to 9 of the SDRmn register with reference to Table 12-3.
• Set the EOCmn and SSECmn bits. This is for enabling or stopping generation of an error interrupt (INTSRE0) when
a communication error occurs.
• When using the SNOOZE mode function, set the SWCm bit of serial standby control register m (SSCm) to 1 just
before switching to the STOP mode. After the initial setting has completed, set the SSm1 bit of serial channel start
register m (SSm) to 1.
Upon detecting the edge of RxDq (start bit input) after a transition was made to the STOP mode, UART reception is
started.
Cautions 1. The SNOOZE mode can only be used when the high-speed on-chip oscillator clock (f
IH) is selected
for fCLK.
2. The transfer rate in the SNOOZE mode is only 4800 bps.
3. When SWCm = 1, UARTq can be used only when the reception operation is started in the STOP
mode. When used simultaneously with another SNOOZE mode function or interrupt, if the
reception operation is started in a state other than the STOP mode, such as those given below,
data may not be received correctly and a framing error or parity error may be generated.
• When after the SWCm bit has been set to 1, the reception operation is started before the
STOP mode is entered
• When the reception operation is started while another function is in the SNOOZE mode
• When after returning from the STOP mode to normal operation due to an interrupt or other
cause, the reception operation is started before the SWCm bit is returned to 0
4. If a parity error, framing error, or overrun error occurs while the SSECm bit is set to 1, the PEFmn,
FEFmn, or OVFmn flag is not set and an error interrupt (INTSREq) is not generated. Therefore,
when the setting of SSECm = 1 is made, clear the PEFmn, FEFmn, or OVFmn flag before setting
the SWC0 bit to 1 and read the value in bits 7 to 0 (RxDq register) of the SDRm1 register.
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