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15.9.2 Operation in synchronous mode (operation mode 2)
When the UART is used in operation mode 2 (normal mode), the transfer mode
becomes clock synchronization.
I Operation in synchronous mode (operation mode 2)
❍ Transfer-data format
In synchronous mode, data is transferred in units of eight bits LSB first without the start bit and
stop bit appended. Figure 15.9-5 "Transfer-data format (operation mode 2)" shows the data
format in clock synchronization mode.
Send-data write
Send and receive clock
RXE, TXE
Send and receive data
❍ Clock supply
In clock synchronization mode, a number of clock pulses equal to the number of send and
receive bits must be supplied.
•
With the internal clock (dedicated baud-rate generator or internal timer) is selected, the
synchronization clock for data reception is automatically generated when data is sent.
•
When the external clock is selected, ensure that the output-data register (SODR0-3) on the
sending-side UART has data (SSR0-3: TDRE = 0). Then, clock pulses matching a length of
exactly one byte must be supplied externally. Before sending begins and after sending, the
mark level (H) must always be set.
❍ Error detection
Overrun errors can be detected, but parity errors and frame errors cannot be detected.
Figure 15.9-5 Transfer-data format (operation mode 2)
1
0
LSB
1
1
0
0
1
Data
CHAPTER 15 UART
Mark level
0
MSB
339
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