S1C63558 TECHNICAL MANUAL
EPSON
89
CHAPTER 4: PERIPHERAL CIRCUITS AND OPERATION (Serial Interface)
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 receive
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 ISER 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 trans-
ferred in the receive 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 gener-
ated, the framing error flag FER and the error interrupt factor flag ISER 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 trans-
ferred in the receive 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 generated, the overrun
error flag OER and the error interrupt factor flag ISER 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 trans-
ferred in the receive 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 receive data buffer overlap, it will be recognized as an overrun error.
