PD72042B_15 Datasheet, PDF (12/92 Pages) Renesas Technology Corp – LSI DEVICE FOR Inter Equipment BusTM (IEBusTM) PROTOCOL CONTROL

µPD72042B
2.2.1 Bus Mastership Determination (Arbitration)
Before devices connected to the IEBus can control other devices, they must first acquire the bus. This operation
is called arbitration.
When more than one unit starts transmission at the same time, arbitration determines which of those units is allowed
to use the bus.
When arbitration results in only one device being granted bus mastership, the following bus mastership priority
conditions are used:
Remark Those devices that are defeated in arbitration can automatically enter retransmission mode. (For the
µPD72042B, the number of retransmissions can be set by specifying a value between 0 and 7 in the
MCR register.)
(1) Priority by communication type
Broadcast (one-unit-to-multiple-units communication) takes priority over ordinary communication (one-unit-to-
one-unit communication).
(2) Priority by master address
If the communication type is the same, the smallest master address value has the highest priority.
Example Each master address consists of 12 bits. A unit having master address 000H has the highest priority,
while a unit having master address FFFH has the lowest priority.
2.2.2 Communication Mode
The IEBus supports two communication modes, each having a different transmission speed. Table 2-1 lists the
transmission speed for each communication mode and the maximum number of bytes transmitted within one
communication frame.
Table 2-1 Transmission Speed and Maximum Number of Transmission
Bytes in Each Communication Mode
Communication mode
0
1
Maximum number of transmission
bytes (bytes/frame)
16
32
Effective transmission speed^{Note 1} (Kbps)
fX = 6 MHz^{Note 2}
fX = 6.29 MHz^{Note 2}
Approx. 3.9
Approx. 4.1
Approx. 17
Approx. 18
Notes 1. Effective transmission speed at which the maximum transfer rate is achieved
2. Oscillator frequencies for the µPD72042B
Cautions 1. Before devices connected to the IEBus can perform communication, an appropriate commu-
nication mode must be set. Note that if a master unit and an associated unit (slave unit) have
different communication modes, they will not be able to communicate properly.
2. Communication cannot be performed properly between a unit operating at an oscillator
frequency of 6 MHz and another operating at 6.29 MHz, even when set to the same communication
mode. Units must use the same oscillator frequency to be able to communicate.
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Data Sheet S13990EJ3V0DS