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CHAPTER 18 IEBus CONTROLLER (V850/SC2)
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User’s Manual U15109EJ3V0UD
(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
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 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 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 the data has continuation 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.
(b) When master receives data
When the master unit reads data from a slave unit, the master unit outputs a sync signal corresponding to
all the read bits.
The slave unit outputs the contents of the data and parity bits to the bus in response to the sync signal
from the master unit.
The master unit reads the data and parity bits output by the slave unit, and checks the parity.
If the parity is odd, or if the DR register is storing a receive data, the master unit rejects accepting the data,
and does not output the acknowledge signal. If the maximum number of transmit bytes is within the value
that can be transmitted in one communication frame, the master unit repeats reading the same data.
If the parity is even and the DR register is not storing a receive data, the master unit accepts the data and
returns the acknowledge signal. If the maximum number of transmit bytes is within the value that can be
transmitted in one frame, the master unit reads the next data.