Datasheet

Section 14 IEBus™ Controller (IEB) [H8S/2258 Group]
Rev. 6.00 Mar. 18, 2010 Page 528 of 982
REJ09B0054-0600
Because the TxRDY flag is retained after a reset, the DTC transfer starts when the IETxI is
enabled and the first data for the data field is written to IETBR. The DTC negates the TxRDY
flag and the first byte of DTC transfer is completed.
(3) Master Transmission Flow
Figure 14.8 shows the master transmission flow. Numbers in the following description correspond
to the number in figure 14.8.
1. After the IEB and DTC have been initialized, a master communications request command is
issued from IECMR. During slave reception, the command execution status flag (CMX) in
IEFLG is set and the master communications request will not be issued.
2. When the slave reception has been completed, the CMX flag is cleared, the master
communications command is executed, and the MRQ flag is set.
3. The transmit start detection flag (TxS) in IETSR is set when arbitration is won and the master
address has been transmitted. In this case, one of the transmit status interrupts (IETSI) is
requested to the CPU, and the TxS flag is cleared in the interrupt handling routine.
4. The IEB loads data to be transmitted in the data field from IETBR when the control and
message length fields have been transmitted and an ACK is received in each field. After that,
the TxRDY flag is set. A DTC transfer request is generated by IETxI and the second byte is
written to the transmit buffer.
5. Similarly, the data field load and transmission are repeated.
6. The DTC completes the data transfer for the number of specified bytes when data to be
transmitted in the last byte is written to. At this time, the DTC does not clear the TxRDY flag.
It, however, clears bit DTCEG5 in the DTC enable register G (DTCERG) so as not to generate
more DTC transfer request.
7. A TxRDY interrupt (IETxI) is issued to the CPU when the DTC transfer is completed. In this
interrupt handling routine, the TxRDY flag can be cleared. However, since a TxRDY interrupt
will be generated again after the last byte transfer, the TxRDY flag remains set. (Note that the
LUEE bit must be cleared to 0 because an underrun error occurs to terminate the transfer if the
LUEE bit in IECTR is set to 1.) Note, however, that the TxRDY interrupt must be disabled
because the TxRDY interrupt is always generated.
8. A transmit normal completion (TxF) interrupt (IETSI) occurs after the last data transfer is
completed. In this case, the CPU clears the TxF flag and completes the normal completion
interrupt and clears the MRQ flag to 0.
Note: As a transmit status interrupt (IETSI), the transmit error termination (TxE) interrupt as
well as the transfer start detection (TxS) and transmit normal completion (TxF) interrupts
must be enabled. If an error termination interrupt is disabled, no interrupt is generated
even if the transmission is terminated by an error.