Determining Bus Mastership (Arbitration); Communication Mode; Table 13.4.3A Transfer Rate And Maximum Number Of Transfer Byte In Each Communication Mode - Fujitsu F2MC-16LX MB90580 Series Hardware Manual

13.4 IEBus Communication Protocol

13.4.2 Determining bus mastership (arbitration)

The equipment connected to the IEBus performs an operation to occupy the bus when it controls another
equipment. This operation is called arbitration.
Arbitration is to grant the bus mastership to one of several units that have simultaneously started
transmission. As only one equipment acquires the bus mastership as a result of arbitration, the following
priority is used to determine which equipment acquires the bus mastership:
• Priority on type of communication
Multiaddress communication takes precedence over normal communication.
• Priority on master address
If the type of communication is the same, the lower master address takes precedence over the higher
one.
Example: The master address consists of 12 bits, the unit at 000H has the highest priority, and the unit
at FFFH has the lowest priority.

13.4.3 Communication mode

The IEBus provides three communication modes, in which each has a different transfer rate. The transfer
rate in each communication mode and the maximum number of transfer bytes in one communication frame
are shown as below:

Table 13.4.3a Transfer rate and maximum number of transfer byte in each communication mode

Maximum number of transfer bytes
Mode
0
1
2
Note1: Effective transfer rate is measured when the maximum number of data bytes have
been transferred.
Note2: The relationship between IEBus internal clock and CPU clock is referred to
Table 13.3.2d.
Caution1: The required communication mode should be selected for each equipment
connected to the IEBus before communication is started. Also, the communication
is not performed correctly unless the communication mode of the master and the
slave unit are the same.
Caution2: Be sure that both the communication mode and IEBus internal clock are the same
for all units connected to the IEBus. Even though the same communication mode
is selected, the communication is still performed incorrectly if the IEBus internal
clock frequency is different.
164 Chapter 13: IE Bus
(bytes / frame)
16
32
128
Effective transfer rate (bps)
IEBus internal clock =
Note2
6MHz
approx. 3.9Kbps
approx. 17Kbps
approx. 26Kbps
Note1
IEBus internal clock =
Note2
6.29 MHz
approx. 4.1 Kbps
approx. 18 Kbps
approx. 27Kbps
MB90580 Series