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Chapter 13
Serial Interface Function
Preliminary User’s Manual U15839EE1V0UM00
(4)
Reception buffer registers (RXB0, RXB1)
The RXBn register is an 8-bit buffer register for storing parallel data that had been converted by
the reception shift register.
When reception is enabled (RXE bit = 1 in the ASIMn register), receive data is transferred from the
reception shift register to the RXBn register, synchronized with the completion of the shift-in
processing of one frame. Also, a reception completion interrupt request (INTSRn) is generated by
the transfer to the RXBn register. For information about the timing for generating this interrupt
request, refer to 13.2.5 (4)“Receive operation” on page 380.
If reception is disabled (RXE bit = 0 in the ASIMn register), the contents of the RXBn register are
retained, and no processing is performed for transferring data to the RXBn register even when the
shift-in processing of one frame is completed. Also, no reception completion interrupt is
generated.
When 7 bits is specified for the data length, bits 6 to 0 of the RXBn register are transferred for the
receive data and the MSB (bit 7) is always 0. However, if an overrun error (OVE) occurs, the
receive data at that time is not transferred to the RXBn register.
Except when a reset is input, the RXBn register becomes FFH even when Power bit = 0 in the
ASIMn register.
This register is read-only in 8-bit or 1-bit units (n = 0, 1).
Figure 13-5:
Reception Buffer Registers (RXB0, RXB1)
7
6
5
4
3
2
1
0
Address
Initial
value
RXB0
RXB7
RXB6
RXB5
RXB4
RXB3
RXB2
RXB1
RXB0
FFFF FA02H
FFH
RXB1
RXB7
RXB6
RXB5
RXB4
RXB3
RXB2
RXB1
RXB0
FFFF FA42H
FFH
Bit Position
Bit Name
Function
7 to 0
RXB7 to
RXB0
Stores receive data.
0 can be read for RXB7 when 7-bit or character data is received.
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