R8C/20 Group, R8C/21 Group 21. Usage Notes
Rev.2.00 Aug 27, 2008 Page 444 of 458
REJ09B0250-0200
21.4 Notes on Serial Interface
• When reading data from the UiRB (i = 0 or 1) register even in the clock asynchronous serial I/O mode or in the
clock synchronous serial I/O mode. Ensure to read data in 16-bit unit. When the high-order byte of the UiRB
register is read, the PER and FER bits in the UiRB register and the RI bit in the UiC1 register are set to 0.
To check receive errors, read the UiRB register and then use the read data.
Example (when reading receive buffer register):
MOV.W 00A6H,R0 ; Read the U0RB register
• When writing data to the UiTB register in the clock asynchronous serial I/O mode with 9-bit transfer data
length, write data high-order byte first, then low-order byte in 8-bit units.
Example (when reading transmit buffer register):
MOV.B #XXH,00A3H ; Write the high-order byte of U0TB register
MOV.B #XXH,00A2H ; Write the low-order byte of U0TB register
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