UPD784938 Datasheet, PDF (478/733 Pages) NEC – 16-Bit Single-Chip Microcontrollers

CHAPTER 20 IEBus CONTROLLER
(2) Lock address
When the lock address is read (control bit: 4H or 5H), the address (12 bits) of the master unit that has issued the lock
instruction is configured in 1-byte units as shown below and read.
Figure 20-8. Configuration of Lock Address
MSB
LSB
Control bit: 4H
Low-order 8 bits
Control bit: 5H
Undefined
High-order 4 bits
(3) Data
If the control bit indicates reading of data (3H or 7H), the data in the data buffer of the slave unit is read by the master
unit.
If the control bit indicates writing of data (BH or FH), the data received by the slave unit is processed according to the
operation rule of that slave unit.
(4) Locking and unlocking
The lock function is used when a message is transferred in two or more communication frames.
The unit that is locked does not receive data from units other than the one that has locked the unit.
A unit is locked or unlocked as follows:
<1> Locking
If the communication frame is completed without succeeding in transmission or reception of the data of the number
of bytes specified by the telegraph length bit after the acknowledge bit ‘0’ of the telegraph length field has been
transmitted or received by the control bit that specifies locking (3H, AH, or BH), the slave unit is locked by the
master unit. At this time, the bit (bit 2) in the byte indicating the slave status is set to ‘1’.
<2> Unlocking
After transmitting or receiving data of the number of data bytes specified by the telegraph length bit in one
communication frame by the control bit that has specified locking (3H, AH, or BH), or the control bit that has
specified unlocking (6H), the slave unit is unlocked by the master unit. At this time, the bit related to locking (bit
2) in the byte indicating the slave status is reset to ‘0’.
Locking or unlocking is not performed during broadcasting communication.
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Preliminary User’s Manual U13987EJ1V0UM00