H8SSLASH2224 datasheet(629/1071 Pages) RENESAS

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Section 14 IEBus™ Controller (IEB) [H8S/2258 Group]

Rev. 5.00 Aug 08, 2006 page 543 of 982

REJ09B0054-0500

(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.

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