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4.1 Auto-Flow Mode
In auto-flow mode, the connected devices are also assumed to operate in auto-flow mode. If a connected device
does not stop transmission by pulling RTSZ high, an overrun error occurs.
(1) HCR0 software reset
Almost all UART interface registers are initialized by setting bit 7 of the HCR0 register to 1, except for the
FIFOs.
(2) Error detection when a FIFO is used
A parity error, framing error, and break interrupt are detected during reception and error information is
concurrently stored in the FIFO with the data. Next, an interrupt is reported when data 1 byte or 2 bytes before
the data that caused the error is read out. No break interrupt occurs when no start bit is detected (such as
during frame data reception). However, the break interrupt can be detected in the non-FIFO mode. If the
above errors are detected while a FIFO is used, the receive FIFO must be reset by using bit 1 of the FCR
register to clear error information in the FIFO.
(3) Interrupt signal (INTRPT)
After the INTRPT signal related to data transfer is pulled high, it stays at high level until the interrupt source is
cleared. However, the transmit buffer empty interrupt is masked by reading the IIR register. The mask is
disabled by writing data to transmit. After the transmit buffer empty interrupt is masked, it does not occur even
if the transmit buffer is empty, as long as data to transmit is not written.
(4) Serial clock generation
A serial clock is masked after a reset. The mask is disabled by setting up the baud rate registers (DLL and
DLM) and then setting bit 7 (DLAB) of the LCR register to 0. Because the mask is disabled at the falling edge
of the output of the DLAB bit setting, disabling the mask is valid only once after a reset. The masking can be
specified only when hardware is reset.
(5) Auto-flow mode is disabled when bit 3 of the IER register is set to 1
When the modem status interrupt is enabled,
auto-CTS : disabled
auto-RTS : enabled
To enable auto-flow mode, the modem status interrupt must therefore be disabled.
CHAPTER 4 DESCRIPTION OF FUNCTIONS
User's Manual S19262EJ3V0UM
37
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