HD404639R Datasheet, PDF (89/135 Pages) Renesas Technology Corp – 4-Bit Single-Chip Microcomputer

HD404639R Series
Transmit Clock Error Detection (In External Clock Mode): Each serial interface will malfunction if a
spurious pulse caused by external noise conflicts with a normal transmit clock during transfer. A transmit
clock error of this type can be detected as shown in figure 69.
If more than eight transmit clocks are input in transfer state, at the eighth clock including a spurious pulse
by noise, the octal counter reaches 000, the serial 1 interrupt request flag (IFS1: $003, bit 2) is set, and
transmit clock wait state is entered. At the falling edge of the next normal clock signal, the transfer state is
entered. After the transfer is completed and IFS1 is reset, writing to serial mode register 1A (SM1A: $005)
changes the state from transfer to STS wait. At this time serial interface 1 is in the transfer state, and the
serial 1 interrupt request flag is set again, and therefore the error can be detected. The same applies to serial
interface 2.
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