CHAPTER 19 IEBus CONTROLLER (V850/SB2)
User’s Manual U13850EJ4V0UM
466
(7) IEBus data register (DR)
The IEBus data register (DR) sets the communication data. Sets the communication data (8 bits) to bits 7 to
0.
Remark
The IEBus data register consists of a write register and a read register. Consequently, data written
to this register cannot be read as is. The data that can be read is the data received during IEBus
communication.
(a) When transmission unit
The data (1 byte) written to the IEBus data register (DR) is stored to the IEBus interface shift register of
the IEBus. It is then output from the most significant bit, and an interrupt (INTIE1) is issued to the CPU
each time 1 byte has been transmitted. If NACK is received after 1-byte data has been transferred
during individual transfer, data is not transferred from DR to the shift register, and the same data is
retransmitted. At this time, INTIE1 is not generated. INTIE1 is issued when the IEBus interface shift
register stores the IEBus data register value. However, when the last byte and 32nd byte (the last byte
of 1 communication frame) is stored in the shift register, INTIE1 is not issued.
(b) When reception unit
One byte of the data received by the shift register of the IEBus interface block is stored to this register.
Each time 1 byte has been correctly received, an interrupt (INTIE1) is issued.
When transmit/receive data is transferred to and from the IEBus data register, using DMA can reduce the
CPU processing load.
Figure 19-21. IEBus Data Register (DR) Format
After reset: 00H
R/W
Address: FFFFF3ECH
7
6
5
4
3
2
1
0
DR
Cautions 1. If the next data is not in time while the transmission unit is set, an underrun occurs, and a
communication error interrupt (INTIE2) occurs, stopping transmission.
2. When the IEBus is a receiving unit, if the reading of the data is too late for the next data
reception timing, the unit will enter the overrun state. At this time, during individual
communication reception, NACK will be returned at the acknowledge bit of the data field,
and the master unit will be requested to retransmit the data. If an overrun error occurs
during broadcasting communication, the communication error interrupt (INTIE2) is
generated.
Содержание MPD703030A
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