NEC PD750008 User Manual
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µPD750008 USER'S MANUAL
<4> RESET command
The RESET command changes the currently selected slave to a non-selected slave. When
a RESET command is transmitted, any slave can be placed in the non-selected state.
Figure 5-77. Transfer Format of the RESET Command
Remark M: Output by the master
S: Output by the slave
<5> CHGMST command
The CHGMST command passes the master authority to the currently selected slave.
Figure 5-78. Transfer Format of the CHGMST Command
Remark M: Output by the master
S: Output by the slave
When the slave receives a CHGMST command, the slave returns one of the following data
to the master after checking whether the slave can receive the master authority:
• 0FFH: Master changeable
• 00H: Master not changeable
The slave compares the contents of SIO before transfer with the contents of SIO after transfer.
If the contents of SIO disagree with each other, an error occurs; ACK is not returned in this
case.
If the master receives 0FFH, the master returns ACK to the slave, and starts to operate as
a slave. The slave which transmitted 0FFH starts to operate as the master when it receives
ACK.
(iv) Error occurrence
If a communication error occurs, the operation described below is performed.
The slave reports the occurrence of an error by not returning ACK to the master. If an error
occurs during reception of data, the slave sets the status bit for indicating error occurrence,
and cancels all command processing being performed.
When the transmission of one byte is completed, the master checks for ACK from the slave.
CHGMST
M
ACK
S
Command
Data
S
ACK
S
Data
RESET
M
ACK
S
Command