CHAPTER 19 SERIAL INTERFACE UNIT 1 (SIU1)
User’s Manual U14272EJ3V0UM
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• FIFO interrupt modes
When receive FIFO is enabled and receive interrupt requests are enabled, receive interrupts can occur as
described below.
1. When the FIFO is reached to the specified trigger level, a receive data ready interrupt request is notified
to the CPU.
This interrupt is cleared when the FIFO goes below the trigger level.
2. When the FIFO is reached to the specified trigger level, the SIUIID_1 register indicates a receive data
ready interrupt request.
Same as the interrupt above, the SUIID_1 register is cleared when the FIFO goes below the trigger level.
3. The receive line status interrupt is assigned to a higher priority level than the receive data ready interrupt.
4. When characters are transferred from the shift register to the receive FIFO, 1 is set to the LSR0 bit of the
SIULS_1 register.
The value of this bit returns to 0 when the FIFO becomes empty.
When receive FIFO is enabled and receive interrupts are enabled, receive FIFO timeout interrupt requests can
occur as described below.
1. Followings are the conditions under which FIFO timeout interrupt requests occur.
• At least one character is being stored in the FIFO.
• The time required for sending four characters has elapsed since the serial reception of the last
character (includes the time for the second stop bit in cases where it is specified that two stop bits are
required).
• The time required for sending four characters has elapsed since the last read of the FIFO by the CPU.
The time between receiving the last character and issuing a timeout interrupt request is a maximum of
160 ms when operating at 300 baud and receiving 12-bit data.
2. The transfer time for a character is calculated based on the baud rate clock for reception (internal) (which
is why the elapsed time is in proportion to the baud rate).
3. Once a timeout interrupt request has occurred, the timeout interrupt is cleared and the timer is reset as
soon as the CPU reads one character from the receive FIFO.
4. If no timeout interrupt request has occurred, the timer is reset when a new character is received or when
the CPU reads the receive FIFO.
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