
CHAPTER 18 IEBus CONTROLLER
User’s Manual U17790EJ2V0UD
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(7) Data field
This is data output by the transmission side.
The master unit transmits or receives data to or from a slave unit by using the data field.
The configuration of the data field is as shown below.
Figure 18-6. Data Field
Data field (number specified by telegraph length field)
MSB
LSB
One data
ACK
Parity
Data bit (8 bits)
ACK
Parity
Following the data bit, the parity bit and acknowledge bit are respectively output by the master unit and slave
unit.
Use broadcast communication only for when the master unit transmits data. At this time, the acknowledge bit
is ignored.
The operation differs as follows depending on whether the master transmits or receives data.
(a) When master transmits data
When the master units writes data to a slave unit, the master unit transmits the data bit and parity bit to the
slave unit. If the parity is even and the receive data is not stored in the DR register when the slave unit
has received the data bit and parity bit, the slave unit outputs an ACK signal. If the parity is odd or if the
receive data is stored in the DR register, the slave unit rejects receiving the data, and outputs the NACK
signal.
If the slave unit outputs the NACK signal, the master unit transmits the same data again. This operation
continues until the master detects the ACK signal from the slave unit, or the data exceeds the maximum
number of transmit bytes.
If there is more data and the maximum number of transmit bytes is not exceeded when the parity is even
and when the slave unit outputs the ACK signal, the master unit transmits the next data.
During broadcast communication, the slave unit outputs the NACK signal, and the master unit transfers 1
byte of data at a time. If the parity is odd or the DR register is storing receive data after the slave unit has
received the data bit and parity bit during broadcast communication, the slave unit judges that reception
has not been performed correctly, and stops reception.