UPD784938 Datasheet, PDF (475/733 Pages) NEC – 16-Bit Single-Chip Microcontrollers

CHAPTER 20 IEBus CONTROLLER
The operation differs as follows depending on whether the master transmits or receives data.
<1> 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 receive data is not stored in the data register (DR) when the slave unit receives
the data bit and parity bit, the slave unit outputs an acknowledge signal. If the parity is odd or if receive data
is stored in the 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 is continuous 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. During broadcast communication, the slave unit receives the data and parity
bits, and if the parity is odd or receive data is stored in the DR, reception is considered not to have been performed
correctly and is stopped.
<2> 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 the DR is receiving data, the master unit refuses to acknowledge this data and does not
output the acknowledge signal. If the maximum number of transmit bytes is a value within the range that can
be transmitted in one communication frame, the master unit repeats reading the same data.
If the parity is even and the DR is not receiving 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.
(8) Parity bit
The parity bit is used to confirm that 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 the 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 confirm that 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).
• ‘1’: Indicates that the transmit data is not recognized (NACK).
Preliminary User’s Manual U13987EJ1V0UM00
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