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MB90420/5 (A) SERIES F
12.8 Precautions at Using UART
Precautions at using the UART are shown below.
n Precautions at using UART
• Operation enable
The control register (SCR0/1) of the UART has the operation enable bits, TXE and RXE to transmit and
receive, respectively. The default (initial value) is both the transmission and reception are disabled, so
they must be enabled before transferring data. Also, they can be disabled as necessary to cancel data
transfer.
• Setting of communication mode
Set the communication mode when data transfer is stopped. If the communications mode is set during
data transmission/reception, those data are not assured.
• Synchronous mode
The clock synchronous mode (operation mode 2) of the UART uses the clock control (I/O ecpansion serial)
mode; the start and stop bits are not affixed to the data.
• Timing of transmit interrupt enable
Since the default (initial value) of the transmit data empty flag bit (SSR0/1: TDRE) is 1 (no transmit data
and transmit data write enabled), when the transmit interrupt request is enabled (SSR0/1: TIE = 1), the
transmit interrupt request is issued immediately. Always set the TIE flag to 1 after preparation of the
transmit data.
• Reception in multiprocessor mode
The 9-bit reception cannot be performed in the UART multiprocessor mode.
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MC-16LX FAMILY 16-BIT MICROCONTROLLERS HARDWARE MANUAL
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