
CHAPTER 18 IEBus CONTROLLER
User’s Manual U17790EJ2V0UD
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(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 outputs the NACK 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
outputs the ACK 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 broadcast 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’.
(9) Acknowledge bit
During normal communication (communication from one unit to another), an acknowledge bit is appended to
the following locations to check if the data has been correctly received.
End of slave address field
End of control field
End of telegraph length field
End of data field
The definition of the acknowledge bit is as follows.
0: Indicates that the transmit data is recognized (ACK signal).
1: Indicates that the transmit data is not recognized (NACK signal).
During broadcast communication, however, the contents of the acknowledge bit are ignored.
(a) Last acknowledge bit of slave field
The last acknowledge bit of the slave field serves as a NACK signal in any of the following cases, and
transmission is stopped.
If the parity of the master address bit or slave address bit is incorrect
If a timing error (error in bit format) occurs
If a slave unit does not exist