SH7708 datasheet(436/633 Pages) RENESAS

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Switching Modes: When switching from receive mode to transmit mode, check that the receive

operation is completed before starting initialization and setting RE to 0 and TE to 1. The RDRF,

PER, and ORER flags can be used to check if reception is completed. When switching from

transmit mode to receive mode, check that the transmit operation is completed before starting

initialization and setting TE to 0 and RE to 1. The TEND flag can be used to check if transmission

is completed.

Interrupt Operation: In the smart card interface mode, there are three types of interrupts:

transmit-data-empty (TXI), communication error (ERI) and receive-data-full (RXI). In this mode,

the transmit-end interrupt (TEI) cannot be requested.

Set the TEND flag in SCSSR to 1 to request a TXI interrupt. Set the RDRF flag in SCSSR to 1 to

request an RXI interrupt. Set the ORER, PER, or FER/ERS flag in SCSSR to 1 to request an ERI

interrupt (table 14.9).

Table 14.9

Smart Card Mode Operating Status and Interrupt Sources

Mode

Status

Flag

Mask Bit

Interrupt Source

Transmit mode

Normal

TEND

TIE

TXI

Error

FER/ERS

RIE

ERI

Receive mode

Normal

RDRF

RIE

RXI

Error

PER,

ORER

RIE

ERI

14.4

Usage Notes

When the SCI is used as a smart card interface, be sure that all criteria in sections 14.4.1 and

14.4.2 are applied.

14.4.1

Receive Data Timing and Receive Margin in Asynchronous Mode

In asynchronous mode, the SCI runs on a basic clock with a frequency of 372 times the transfer

rate. During reception, the SCI samples the fall of the start bit using the base clock to achieve

internal synchronization. Receive data is latched internally on the rising edge of the 186th basic

clock cycle (figure 14.8).

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