H8SSLASH2224 datasheet(628/1071 Pages) RENESAS

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

Rev. 5.00 Aug 08, 2006 page 542 of 982

REJ09B0054-0500

14.6.3

RxRDY Flag and Overrun Error

1. The RxRDY flag indicates that IERBR stores data. Reading from IERBR by the DTC clears

the RxRDY flag. Meanwhile, the RxRDY flag must be cleared by software since reading from

IERBR by the CPU does not clear the RxRDY flag.

2. If the CPU fails to read from IERBR by the timing of the frame reception or if the number of

transfer words is less than the length specified by the message length bits, an overrun error

occurs.

3. The IEB receives data while the RxRDY flag is set and sets the OVE flag when the parity bit

reception starts. If the OVE flag is set when the acknowledge bit is transmitted, the IEB

assumes that an overrun error has occurred, returns a NAK, and discards the data in the receive

shift register.

4. On the transmit side, the unit continues retransfer until an ACK is received because it receives

a NAK.

5. If the OVE flag is cleared without loading the receive data from IERBR in the RxE interrupt

handling routine caused when the OVE flag is set to 1, the IEB decides that the overrun error

has been cleared and sends an ACK to other units. In this case, the transmit unit completes the

communications correctly. However, no receive data is loaded from the IERBR and the receive

unit continues reception. Accordingly, in an interrupt handling routine caused by the OVE flag,

receive data must be loaded from IERBR, the RxRDY flag must be cleared. The DTC, thus,

should be ready to receive the next byte, and then the OVE flag must be cleared.

6. Item 5 above will not occur when the DTC transfer words is specified as the IERBFL value.

14.6.4

Error Flag s in the IETEF

(1) AL Flag

The AL Flag is set to 1 when arbitration is lost even if retransfer is performed for the number of

times specified by IEMCR after arbitration has been lost. The AL flag is not set when arbitration is

won during retransfer. If the AL flag is set to 1, the TxE flag is set and the wait state is entered.

(2) UE Flag

If the UE flag is set to 1, the TxE flag is set and the wait state is entered. For details, see section

14.6.2, TxRDY Flag and Underrun Error.

(3) TTME Flag

If a timing error occurs during data transfer, the TTME and TxE flags are set, and the wait state is

entered.

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