20 GENERAL-PURPOSE SERIAL INTERFACE (FSIO)
S1C33L26 TECHNICAL MANUAL
Seiko Epson Corporation
20-17
In addition, a DMA can be invoked every time the received data is written to the receive-buffer, allowing the
received data to be transferred successively to the specified memory location through DMA transfers.
For details on how to control interrupts/DMA, refer to Section 20.9, “FSIO Interrupts and DMA.”
Figure 20.7.3.2 shows a receive timing chart in the asynchronous mode.
Example: Data length: 8 bits, Stop bit: 1 bit, Parity bit: Included
S1
S2
Start bit
Stop bit
P Parity bit
Receive-buffer full interrupt request
(FIFOINT[1:0] = 2)
Overrun error
interrupt request
Sampling clock
SIN
x
Receive data buffer
RXDNUM[1:0]
RDBF
data 1
S1 D0 ··· P S2 S1 D0 ··· P S2 S1 D0 ··· P S2 S1 D0 ··· P S2 S1 D0 ··· P S2 S1 D0 ··· P
S2
data 2
data 3
data 4
data 5
data 6
S2 S1 D0 ··· P
data 7
data 1
1, 2
2, 3, 4, 5
2, 3, 4
1, 2, 3
2, 3
1
3
2
2
1
0
DMA trigger timings
Data read
7.3.2 Receive Timing Chart in Asynchronous Mode
Figure 20.
1. The serial interface starts sampling when the start bit is input (SIN
x
= low).
2. When the start bit is sampled at the first rising edge of the sampling clock, each bit of receive data is taken
into the shift register, beginning with the LSB at each rising edge of the subsequent clock. This operation is
repeated until the MSB of data is received.
3. When the MSB is taken in, the parity bit that follows is also taken in (if EPR = 1).
4. When the stop bit is sampled, the data in the shift register is transferred to the receive data register, enabling
the data to be read out.
The parity is checked when data is transferred to the receive data register (if EPR = 1).
Note: The receive operation is terminated when the first stop bit is sampled even if the stop bit is config-
ured with two bits.
(3) Receive errors
Three types of receive errors can be detected when receiving data in the asynchronous mode.
Since an interrupt can be generated by setting the interrupt control bits, the error can be processed using an
interrupt processing routine. For details on receive error interrupts, refer to Section 20.9, “FSIO Interrupts and
DMA.”
Parity error
If EPR/FSIO_CTL
x
register is set to 1 (parity added), the parity is checked when data is received.
This parity check is performed when the data received in the shift register is transferred to the receive data buf-
fer in order to check conformity with the PMD/FSIO_CTL
x
register setting (odd or even parity).
If any nonconformity is found in this check, a parity error is assumed and the parity error flag PER/FSIO_STA-
TUS
x
register is set to 1.
Even when this error occurs, the received data in error is transferred to the receive data buffer and the receive
operation is continued. However, the content of the received data for which a parity error is flagged cannot be
guaranteed.
PER is reset to 0 by writing 0.
Framing error
If data with a stop bit = 0 is received, the serial interface assumes that the data is out of synchronization and
generates a framing error.
If two stop bits are used, only the first stop bit is checked.
When this error occurs, the framing-error flag FER/FSIO_STATUS
x
register is set to 1.