UPD72042BGT NEC [NEC], UPD72042BGT Datasheet - Page 20

• Manufacturer Part Number: UPD72042BGT
• Description: LSI DEVICE FOR Inter Equipment Bus (IEBus) PROTOCOL CONTROL
• Manufacturer: NEC [NEC]

(3) Reading a lock address (control bits: 4H, 5H)
(4) Locking and unlocking (control bits: Locking (3H, AH, BH), unlocking (6H))
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When a lock address read operation (4H, 5H) is specified, the address (12 bits) of the master unit that
issued the lock instruction is read in one-byte form, as shown below.
The lock function is used to enable the transfer a message using more than one communication frame.
When locked, a unit cannot receive data from other than the unit that requested the lock.
Locking and unlocking are performed as follows:
1
2
Locking
The master unit can lock the slave unit by specifying the lock with the corresponding control bits (3H, AH,
BH). In this case, when the transmission or reception of acknowledge bit 0 for the data-length field has been
completed, but the communication frame is then terminated before transmission or reception of as many data
bytes as are specified by the data-length bits is completed, the slave unit is locked. At this time, the bit
indicating the lock status (bit 2) in the slave status byte is set to 1.
Unlocking
The master unit can unlock a locked slave unit when the control bits specify locking (3H, AH, or BH) or
unlocking (6H). The slave unit is unlocked once as many data bytes as are specified by the data-length bits
have been transmitted or received within one communication frame. At this time, the bit indicating the lock
status (bit 2) in the slave status byte is reset to 0.
For broadcast, locking or unlocking is not performed.
Control bits : 4H
Control bits : 5H
Fig. 2-3 Lock Address Format
Data Sheet S13990EJ3V0DS
MSB
Undefined
Low-order 8 bits
High-order 4 bits
LSB
PD72042B