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CHAPTER 17
IEBus CONTROLLER (
PD178096A, 178098A, 178F098 ONLY)
User’s Manual U12790EJ2V0UD
(7) Data field
This is data output by the transmission side.
The master unit transmits to or receives data from a slave unit by using the data field.
The configuration of the data field is as shown below.
Figure 17-6. Data Field
Data field (number specified by telegraph length field)
MSB
LSB
One data
ACK
Parity
Control 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 unit 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 IEBus data register (DR) when the
slave unit has received the data bit and parity bit, the slave unit outputs an acknowledge signal. If the parity
is odd or if the receive data is stored in the IEBus data register (DR), the slave unit rejects receiving the data,
and does not output the acknowledge signal.
If the slave unit does not output the acknowledge signal, the master unit transmits the same data again. This
operation continues until the master detects the acknowledge 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 acknowledge signal, the master unit transmits the next data.
During broadcast communication, the slave unit does not output the acknowledge 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.