Data Transmission (Except For Block Transfer Mode) - Hitachi H8S/2378, H8S/2378R Series Hardware Manual

15.7.6

Data Transmission (Except for Block Transfer Mode)

As data transmission in Smart Card interface mode involves error signal sampling and
retransmission processing, the operations are different from those in normal serial communication
interface mode (except for block transfer mode). Figure 15.26 illustrates the retransfer operation
when the SCI is in transmit mode.
1. If an error signal is sampled from the receiving end after transmission of one frame is
completed, the ERS bit in SSR is set to 1. If the RIE bit in SCR is set at this time, an ERI
interrupt request is generated. The ERS bit in SSR should be cleared to 0 before the next
parity bit is sampled.
2. The TEND bit in SSR is not set for a frame for which an error signal is received. Data is
retransferred from TDR to TSR, and retransmitted automatically.
3. If an error signal is not sent back from the receiving end, the ERS bit in SSR is not set.
Transmission of one frame, including a retransfer, is judged to have been completed, and the
TEND bit in SSR is set to 1. If the TIE bit in SCR is set at this time, a TXI interrupt request is
generated. Writing transmit data to TDR transfers the next transmit data.
Figure 15.28 shows a flowchart for transmission. The sequence of transmit operations can be
performed automatically by specifying the DTC or DMAC to be activated with a TXI interrupt
source. In a transmit operation, the TDRE flag is also set to 1 at the same time as the TEND flag in
SSR, and a TXI interrupt will be generated if the TIE bit in SCR has been set to 1. If the TXI
request is designated beforehand as a DTC or DMAC activation source, the DTC or DMAC will
be activated by the TXI request, and transfer of the transmit data will be carried out. The TDRE
and TEND flags are automatically cleared to 0 when data transfer is performed by the DTC or
DMAC. In the event of an error, the SCI retransmits the same data automatically. During this
period, the TEND flag remains cleared to 0 and the DTC or DMAC is not activated. Therefore,
the SCI and DTC or DMAC will automatically transmit the specified number of bytes in the event
of an error, including retransmission. However, the ERS flag is not cleared automatically when an
error occurs, and so the RIE bit should be set to 1 beforehand so that an ERI request will be
generated in the event of an error, and the ERS flag will be cleared.
When performing transfer using the DTC or DMAC, it is essential to set and enable the DTC or
DMAC before carrying out SCI setting. For details on the DTC or DMAC setting procedures,
refer to section 9, Data Transfer Controller (DTC) or section 7, DMA Controller (DMAC).
Rev. 1.0, 09/01, page 689 of 904