Rev. 1.20
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Rev. 1.20
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BS82B12A-3/BS82C16A-3/BS82D20A-3
Touch Key 8-Bit Flash MCU with LED/LCD Driver
BS82B12A-3/BS82C16A-3/BS82D20A-3
Touch Key 8-Bit Flash MCU with LED/LCD Driver
UART Power Down and Wake-up
When the the device system clock is switched off, the UART will cease to function. If the device
executes the
"
HALT
"
instruction and switches off the system clock while a transmission is still
in progress, then the transmission will be paused until the UART clock source derived from the
microcontroller is activated. In a similar way, if the device executes the
"
HALT
"
instruction and
switches off the system clock while receiving data, then the reception of data will likewise be
paused. When the device enters the IDLE or SLEEP Mode, note that the USR, UCR1, UCR2,
transmit and receive registers, as well as the BRG register will not be affected. It is recommended
to make sure first that the UART data transmission or reception has been finished before the
microcontroller enters the IDLE or SLEEP mode.
The UART function contains a receiver RX pin wake-up function, which is enabled or disabled
by the WAKE bit in the UCR2 register. If this bit, along with the UART enable bit, UARTEN, the
receiver enable bit, RXEN and the receiver interrupt bit, RIE, are all set before the device enters the
IDLE0 or SLEEP Mode, then a falling edge on the RX pin will wake up the device from the IDLE0
or SLEEP Mode. Note that as it takes certain system clock cycles after a wake-up, before normal
microcontroller operation resumes, any data received during this time on the RX pin will be ignored.
For a UART wake-up interrupt to occur, in addition to the bits for the wake-up being set, the global
interrupt enable bit, EMI, and the UART interrupt enable bit, UAR
T
E, must also be set. If these two
bits are not set then only a wake up event will occur and no interrupt will be generated. Note also
that as it takes certain system clock cycles after a wake-up before normal microcontroller resumes,
the UART interrupt will not be generated until after this time has elapsed.