UPD784938 Datasheet, PDF (510/733 Pages) NEC – 16-Bit Single-Chip Microcontrollers

CHAPTER 20 IEBus CONTROLLER
20.7 Cautions when Using IEBus Controller
(1) Receiving slave status request
The µPD784938 Subseries operates differently from the µPD784908 Subseries when receiving the slave status
request. The differences are as follows.
Table 20-10 shows the operation (slave status request) of IEBus controller of the µPD784938 Subseries.
Table 20-10. IEBus Controller Operation (Slave Status Request) of µPD784938 Subseries
State of µPD784938
Subseries
Slave Status
Unlocked state
All units
Locked state
Units that have
lock requested
Except units
that have lock
requested
Received Control
Request
0H, 4H, 5H, 6H
Operation During Reception
Data
• ACK return at ACK period of the control field.
• Sets status transmission flag and generates INTIE2.
(2) Data register (DR) read operation
When receiving a unit, after the reception of each byte is completed, a macro-service activated signal (INTIE1) is
generated, and the CPU needs to perform data register (DR) read processing. When this DR read processing is delayed
and the next data reception is completed, DR will be updated. Therefore, DR read processing should be completed
in the period between INTIE1 generation and the next data reception. The maximum holding time from INTIE1
generation to DR read is approximately 390 µs.
The µPD784908 Subseries has 40 bytes of reception buffer. When receiving data when there is no space in the
reception buffer, NACK is returned and a request for data to be retransmitted to the transmission unit is automatically
generated.
Because, in the case of the µPD784938 Subseries (simple IEBus controller), INTIE1 is generated for every 1 byte
reception, that DR needs to be read by interrupt processing (macro service recommendation).
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Preliminary User’s Manual U13987EJ1V0UM00