CHAPTER 19 IEBus CONTROLLER (V850/SB2)
User’s Manual U13850EJ4V0UM
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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 broadcasting 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 broadcasting 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.
Caution Do not operate master reception in broadcasting communication, because the slave unit
cannot be defined and data transfer cannot be performed correctly.
(8) Parity bit
The parity bit is used to check to see if the transmit data has no error.
The parity bit is appended to each data of the master address, slave address, control, telegraph length, and
data bits.
The parity is an even parity. If the number of bits in data that are ‘1’ is odd, the parity bit is ‘1’. If the number
of bits in the data that are ‘1’ is even, the parity bit is ‘0’.
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