UPD784938 Datasheet, PDF (467/733 Pages) NEC – 16-Bit Single-Chip Microcontrollers

CHAPTER 20 IEBus CONTROLLER
20.1 IEBus Controller Function
IEBus (Inter Equipment Bus) is a small-scale digital data transmission system that transmits data between units. To
implement IEBus with the µPD784938 Subseries, external IEBus driver and receiver are necessary because they are not
provided.
The internal IEBus controller of the µPD784938 Subseries is of negative logic.
20.1.1 Communication protocol of IEBus
The communication protocol of the IEBus is as follows:
(1) Multi-master mode
All the units connected to the IEBus can transmit data to the other units.
(2) Broadcasting communication function
Communication between one unit and plural units can be performed as follows:
• Group-unit broadcasting communication: Broadcasting communication to group units
• All-unit broadcasting communication: Broadcasting communication to all units.
(3) Effective transfer rate
The effective transfer rate is in mode 1 (the µPD784938 does not support modes 0 and 2 of effective transfer rate).
• Mode 1: Approx. 17 kbps
Caution Different modes must not be mixed on one IEBus.
(4) Communication mode
Data transfer is executed in half-duplex asynchronous communication mode.
(5) Access control: CSMA/CD (Carrier Sense Multiple Access with Collision Detection)
The priority of the IEBus is as follows:
<1> Broadcasting communication takes precedence over individual communication (communication from one unit to
another).
<2> The lower master address takes precedence.
(6) Communication scale
The communication scale of IEBus is as follows:
• Number of units: 50 MAX.
• Cable length: 150 m MAX. (when twisted pair cable is used)
Caution The communication scale in an actual system differs depending on the characteristics of the cables,
etc., constituting the IEBus driver/receiver and IEBus.
Preliminary User’s Manual U13987EJ1V0UM00
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