Datasheet

Section 14 IEBus™ Controller (IEB) [H8S/2258 Group]
Rev. 6.00 Mar. 18, 2010 Page 541 of 982
REJ09B0054-0600
14.6 Usage Notes
14.6.1 Setting Module Stop Mode
The IEB is enabled or disabled by setting the module stop control register. In the initial state, the
IEB is disabled. After the module stop mode is canceled, registers can be accessed. For details, see
section 24, Power-Down Modes.
14.6.2 TxRDY Flag and Underrun Error
1. The TxRDY flag indicates that IETBR is empty. Writing to IETBR by the DTC clears the
TxRDY flag. Meanwhile, the TxRDY flag must be cleared by software since writing to IETBR
by the CPU does not clear the TxRDY flag.
2. If the CPU fails to write to IETBR by the timing of the frame transmission or if the number of
transfer words is less than the length specified by the message length bits, an underrun error
occurs.
3. The IEB decides that an underrun error occurred when the data is loaded from IETBR to the
transmit shift register while the TxRDY flag is set to 1. In this case, the IEB sets the TxE flag
in IETSR and enters the wait state. The UE flag in IETEF is also set to 1.
4. On the receive side, the unit decides that a timing error has occurred because the
communications are terminated.
5. In data transfer using the DTC, the TxRDY flag in IETSR is not cleared after the last byte data
is transferred to IETBR and a CPU interrupt caused by the DTC interrupt will occur.
If the TxRDY flag is not cleared in this CPU interrupt handling routine, an underrun error will
occur when the last byte data is loaded from IETBR to the transmit shift register. In this case,
if the LUEE bit is cleared to 0 (initial value), no underrun error occurs and the last byte of the
data field is transmitted correctly. (If the LUEE bit is set to 1, an underrun error occurs.)
6. Although the DTC is used as described in item 5, if the number of DTC transfer words is less
than the length specified by the message length bits, the LUEE bit setting is invalid. (The
LUEE bit is valid only when data is transmitted for the number of bytes specified by the
message length bits has been transmitted.) In this case, an underrun error occurs, data is
transmitted for one byte less than the DTC transfer words, and the transfer is terminated by a
transmit error.