E0C88832/88862 TECHNICAL MANUAL
EPSON
59
5 PERIPHERAL CIRCUITS AND THEIR OPERATION (Serial Interface)
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Receive error
During receiving the following three types of errors
can be detected by an interrupt.
(1) Parity error
When writing "1" to the EPR register to select
"with parity check", a parity check (vertical
parity check) is executed during receiving. After
each data bit is sent a parity check bit is sent.
The parity check bit is a "0" or a "1". Even parity
checking will cause the sum of the parity bit
and the other bits to be even. Odd parity causes
the sum to be odd. This is checked on the
receiving side.
The parity check is performed when data
received in the shift register is transferred to the
received data buffer. It checks whether the
parity check bit is a "1" or a "0" (the sum of the
bits including the parity bit) and the parity set
in the PMD register match. When it does not
match, it is recognized as an parity error and the
parity error flag PER and the error interrupt
factor flag FSERR is set to "1".
When interrupt has been enabled, an error
interrupt is generated at this point.
The PER flag is reset to "0" by writing "1".
Even when this error has been generated, the
received data corresponding to the error is
transferred in the received data buffer and the
receive operation also continues.
The received data at this point cannot assured
because of the parity error.
(2) Framing error
In asynchronous transfer, synchronization is
adopted for each character at the start bit ("0")
and the stop bit ("1"). When receiving has been
done with the stop bit set at "0", the serial
interface judges the synchronization to be off
and a framing error is generated. When this
error is generated, the framing error flag FER
and the error interrupt factor flag FSERR are set
to "1". When interrupt has been enabled, an
error interrupt is generated at this point.
The FER flag is reset to "0" by writing "1".
Even when this error has been generated, the
received data for it is loaded into the receive
data buffer and the receive operation also
continues. However, even when it does not
become a framing error with the following data
receipt, such data cannot be assured.
Even when this error has been generated, the
received data corresponding to the error is
transferred in the received data buffer and the
receive operation also continues. However, even
when it does not become a framing error with
the following data receiving, such data cannot
be assured.
(3) Overrun error
When the next data is received before "1" is
written to RXTRG, an overrun error will be
generated, because the previous receive data
will be overwritten. When this error is gener-
ated, the overrun error flag OER and the error
interrupt factor flag FSERR are set to "1". When
interrupt has been enabled, an error interrupt is
generated at this point. The OER flag is reset to
"0" by writing "1" into it.
Even when this error has been generated, the
received data corresponding to the error is
transferred in the received data buffer and the
receive operation also continues.
Furthermore, when the timing for writing "1" to
RXTRG and the timing for the received data
transfer to the received data buffer overlap, it
will be recognized as an overrun error.
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Timing chart
Figure 5.7.7.4 show the asynchronous transfer
timing chart.
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