Datasheet

Section 14 IEBus™ Controller (IEB) [H8S/2258 Group]
Rev. 6.00 Mar. 18, 2010 Page 543 of 982
REJ09B0054-0600
(4) RO Flag
When retransfer is performed up to the maximum number of transfer bytes defined by the protocol
because of reception of a NAK from the receive side during data field transmission, the number of
transferred bytes may be less than that of bytes specified by the message length. At this time the
RO flag is set. Moreover, when the value of the message length bits is greater than the maximum
number of transfer bytes, the RO flag is also set. The RO flag is not set if the maximum number of
transfer bytes defined by the protocol is specified (for example, 32-byte message length is
specified in mode 1) and the transfer is performed correctly.
If the RO flag is set to 1, the TxE flag is set to 1 and the wait state is entered.
(5) ACK Flag
• If a NAK is received in an acknowledge bit before the message length field transmission, the
ACK flag is set, the TxE flag is set, and then the wait state is entered.
• If a NAK is received in an acknowledge bit of the data field, data is automatically
retransmitted up to the maximum number of transfer bytes defined by the protocol. If an ACK
is received in an acknowledge bit during retransfer and the following data is transmitted
correctly, the ACK flag is not set. If a NAK is received in the last data transfer during the
retransfer for the maximum number of transfer bytes, the ACK flag is set to 1 and the wait
state is entered.
Note: Even if a NAK is received from the receive side during the data field transmission,
retransfer is performed up to the maximum number of transfer bytes defined by the
protocol, and the number of transferred bytes is less than that of bytes specified by the
message length bits, an ACK may be received in the acknowledge bit in the last data
transfer. In this case, the ACK flag is not set although the RO flag is set.
14.6.5 Error Flags in IEREF
(1) OVE Flag
When the OVE flag is set, the RxE flag is also set. If an overrun error is cleared and the OVE flag
is also cleared, the IEBus receive operation is continued. For details, see section 14.6.3, RxRDY
Flag and Overrun Error.
(2) RTME Flag
If a timing error occurs during data reception after reception starts (the RxS flag is set to 1), the
RTME flag is set to 1, RxE flag is set to 1, and the wait state is entered. When a timing error
occurs before reception starts, this flag is not set and the reception frame is discarded.