
362
CHAPTER 13 UART
r Transfer Data Format
In synchronous mode, 8-bit data is transferred in LSB first mode.
Figure 13.7-5 Transfer Data Format (Operation Mode 2)
r Clock Supply
In clock synchronous (I/O extended serial) mode, as many clocks as the number of
transmission/reception bits need to be supplied.
If the internal clock is selected, a data reception synchronous clock is generated when data
is received.
If an external clock is selected, a clock for exactly one byte needs to be supplied from an
external source after making sure that the output data register (SODR0/SODR1) on the
sending side UART contains data (SSR0/SSR1: TDRE="0"). The mark level "H" must be
retained before transmission starts and after it is completed.
r Error Detection
Only overrun errors can be detected, and parity and framing errors cannot be detected.
r Initialization
The following shows the values to be set to use synchronous mode:
[Mode register (SMR0/SMR1)]
MD1, MD0: Set "10B".
CS2, CS1, CS0: Specify the clock input of the clock selector.
SCKE: Set "1" for the dedicated baud rate generator or the internal clock. Set "0" for the
clock output or an external clock.
SOE: Set "1" for transmission. Set "0" for reception.
[Control register (SCR0/SCR1)]
PEN: Set "0".
P, SBL, A/D: These bits make no sense.
CL: Set "1" (8-bit data).
REC: Set "0" (Clear all error flags for initialization).
RXE, TXE: Set "1" to either of the bits.
[Status register (SSR0/SSR1)]
RIE: Set "1" to use interrupts and "0" to not use interrupts.
TIE: Set "1" to use interrupts and "0" to not use interrupts.
Transmission data writing
10
01
1
0
1
Mark level
Transmission/reception clock
RXE, TXE
Send/receive data
LSB
MSB
Data