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(g) Overrun error - supplementary details
(i) When the frame ends in the overrun state during individual communication reception
If the DR register is not read after entering the overrun state and the retransmitted data reaches the
maximum number of bytes (32 bytes), the frame end interrupt (INTIE2) is generated. The overrun
state is maintained until the DR register is read after the end of the frame.
(ii) If the next reception is started in the case of (i) above, or if the next reception is started
without the DR register being read after the final data has been received, regardless of
whether the communication is broadcasting or individual
Even if communication to the IEBus unit starts in the overrun state, the cause of the overrun, NACK,
is not returned in the ACK period of the slave address, control, or telegraph length field (the DR
register is not updated). If the next communication is not to the IEBus unit, the DR register is not
updated until it is read. Because the IEBus unit is not a communication target, the data interrupt
(INTIE1) and communication error interrupt (INTIE2) are not generated.
(iii) If the next transmission occurs in the overrun state
The data to be transmitted next in the overrun state can be no more than 2 bytes long.
Because the data request interrupt (INTIE1) is not generated, the transmit data cannot be set,
resulting in an underrun error. Therefore, clear the overrun status before starting transmission.
(iv) Overrun state release
The overrun state can only be released by reading the DR register or by a system reset. Therefore,
be sure to read DR in a communication error interrupt processing program.
CHAPTER 19
IEBus CONTROLLER (V850/SB2)
User's Manual U13850EJ6V0UD
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