SH7760 Datasheet, PDF (729/1345 Pages) Renesas Technology Corp – SuperHTM RISC engine

Single buffer mode assumes to carry out a predefined number of byte transfers. The current circuit
fetches the value of the FSB bit when the last bit of one byte is transmitted or received, and
proceeds to the STOP operation. Consequently, to stop communications after the transfer of a
specified number of bytes, the FSB bit should be set to 1 before the last byte is transferred.
This timing, however, contains a problem. In transmission mode, FSB is set to 1 BEFORE an
ACK/NACK to the last byte is checked. For this, the following software actions are required.
• Software Actions
The FSB bit must be set before the last eight bits are transmitted or received as mentioned
above. In the case of transmission, ACK/NACK to the last byte needs to be checked. For
example, the software should operate as follows.
In master transmitter mode, the software checks the MST (transmission end) bit by interrupt or
polling after the last byte is set. At the same time, it checks MNR (master NACK received). If
NACK is returned, it makes a branch to the error routine where the last byte is retransmitted.
In master receiver mode, the software ends reception after confirming that the last byte has
been received. However, if the last byte has any defect, it issues a retransmission request by
the upper protocol.
Rev. 1.0, 02/03, page 679 of 1294