UPD784938 Datasheet, PDF (477/733 Pages) NEC – 16-Bit Single-Chip Microcontrollers

CHAPTER 20 IEBus CONTROLLER
20.1.7 Transmit data
(1) Slave status
The master unit can learn why the slave unit did not return the acknowledge bit (ACK), by reading the slave status.
The slave status is determined depending on the result of the last communication the slave unit has executed.
All the slave units can supply information on the slave status.
Table 20-6 shows the meaning of the slave status.
MSB
Bit 7
Figure 20-7. Bit Configuration of Slave Status
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
LSB
Bit 0
Table 20-6. Meaning of Slave Status
Bit
Bit 0^{Note 1}
Bit 1^{Note 2}
Bit 2
Bit 3
Bit 4^{Note 3}
Bit 5
Bit 7
Bit 6
Value
Meaning
0 Transmit data is not written to data register (DR)
1 Transmit data is written to DR
0 Receive data is not saved to DR
1 Receive data is saved to DR
0 Unit is not locked
1 Unit is locked
0 Fixed to ‘0’
0 Slave transmission is stopped
1 Slave transmission is ready
0 Fixed to ‘0’
00 Mode 0
Indicates highest mode supported by unit^{Note 4}
01 Mode 1
10 Mode 2
11 Not used
Notes 1. The value of this buffer of the µPD784938 Subseries is initialized to 1 at reset.
2. The receive buffer of the µPD784938 Subseries has a capacity of 1 byte.
3. When the µPD784938 Subseries serves as a slave unit, this bit corresponds to the status indicated by bit
4 (ENSLVTX) of the bus control register (BCR).
4. When the µPD784938 Subseries serves as a slave unit, bits 7 and 6 are fixed to ‘0’ and ‘1’ (mode 1),
respectively.
Preliminary User’s Manual U13987EJ1V0UM00
477