NEC mPD780852 Series Preliminary User's Manual page 191

(2) Serial receive data buffer status register (SRBS2)
This register is used to indicate the status of serial receive data buffer register (SIRB2).
SRBS2 is set with an 8-bit memory manipulation instruction.
RESET input clears SRBS2 to 00H.
Figure 14-4. Serial Receive Data Buffer Status Register (SRBS2) Format
Address: FF9AH After Reset: 00H
Symbol 7
SRBS2 0
SDVA
0
1
SDOF
0
1
Cautions 1. When an overflow error occurs, receive data in SIO2 will not be transferred to SIRB2
even if the next receive operation for SIO2 is complete.
2. When an overflow error occurs, be sure to read SRBS2 (clear SDOF), and read SIRB2
(clear SDVA). If the receive operation is resumed without reading SIRB2 (clearing
SDVA) after SDOF clear, SDOF is set even if the next receive operation ends normally.
3. Even if an overflow error has occurred, new receive data can be received by SIO2. At
this time, a transmit completion interrupt (INTCSI2) occurs.
(a) Serial data valid flag (SDVA)
This flag indicates that the serial receive data buffer register (SIRB2) has not been completely read. It is
set to 1 when the receive data has been completely transferred from the serial I/O shift register 2 (SIO2)
to SIRB2.
SDVA is cleared to 0 when SIRB2 has been read. If SIRB2 is accessed for read, SDVA remains cleared
(to 0) until the next receive data is transferred from SIO2 to SIRB2.
(b) Overflow flag (SDOF)
This flag indicates whether an overflow error occurs on the serial receive data buffer register (SIRB2).
It is automatically set to 1 to prevent a loss of receive data if data that has not yet been read remains in
SIRB2 (SDVA = 1) and if the next data has been transferred to SIO2.
CHAPTER 14 SERIAL INTERFACE SIO2
R
6 5
0 0
Receive Data Status Check
All data in SIRB2 has been read.
This bit is cleared to 0 when SIRB2 has been read.
Data in SIRB2 has not been read.
This bit is set to 1 when all receive data has been transferred from SIO2 to SIRB2.
Overflow Check When Serial Data Is Transferred
No overflow error. All data in SIRB2 has been read.
This bit is cleared to 0 when SIRB2 has been read.
Overflow error occurs.
This bit is set to 1 if receive data is set in SIRB2 and if the next reception operation has
been completed before that data is read (if data is transferred to SIO2).
Preliminary User's Manual U14581EJ3V0UM00
4 3 2
0 0 0
1 0
SDVA SDOF
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