Fujitsu FR81S Manuale Utente
CHAPTER 40: MULTI-FUNCTION SERIAL INTERFACE
5. Operation of UART
FUJITSU SEMICONDUCTOR LIMITED
CHAPTER : MULTI-FUNCTION SERIAL INTERFACE
FUJITSU SEMICONDUCTOR CONFIDENTIAL
152
5.2.3.
Reception Operation
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When reception operation is enabled (SCR:RXE=1), the reception operation will start.
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When a start bit is detected, one frame data will be received according to the data format set in the
extended communication control register (ESCR:PEN, P, L2, L1, L0) and serial mode register
(SMR:BDS). The start bit is detected when the falling edge (at ESCR:INV="0") or the rising edge (at
ESCR:INV="1") is detected after data passes the noise filter (majority decision by sampling the serial
data input with the bus clock three times), and the passed data detects "L" at the sampling point.
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When the reception of one frame data has completed, the reception data full flag bit (SSR:RDRF) will be
set to "1". If reception interrupts are enabled (SCR:RIE=1) at this time, a reception interrupt occurs.
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When you read a reception data, do it after the one frame data reception has completed, and check for the
state of error flag of the serial status register (SSR). When a reception error has detected, correct the
error.
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After a read of reception data, the reception data full flag bit (SSR:RDRF) will be cleared to "0".
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When reception FIFO is enabled, if as many frames as set in the reception FBYTE have been received,
the reception data full flag bit (SSR:RDRF) will be set to "1".
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In the case where all the conditions below are met, when reception idle continues for more than 8 baud
rate clocks, interrupt flag (RDRF) will be set to "1".
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Reception FIFO idle detection enable bit (FRIIE) is "1"
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Data count contained in the reception FIFO does not reach the transfer count
If you read the RDR while the counter is counting 8 baud rate clocks, the counter will be reset to 0 and
start counting 8 clocks again. When reception FIFO is disabled, the counter will be reset to "0". When the
reception FIFO is enabled while any data is left in the reception FIFO, counting will be started once
again.
When the reception FIFO is enabled, if the error flag of the serial status register (SSR) is set to"1", the
erroneous data will not be stored in the reception FIFO. Also, the reception data full flag bit (SSR:RDRF)
at that time will not be set to "1". (However, when an overrun error does occur, the flag will be set to
"1".) The reception FBYTE indicates the number of data which have been successfully received before
the error occurs. Unless the error flag of the serial status register (SSR) is cleared to "0", the reception
FIFO will not be enabled.
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When the reception FIFO is enabled, if the reception FIFO has no more data, the reception data full flag
bit (SSR:RDRF) will be cleared to "0".
Notes:
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The data on the receive data register (RDR) will be enabled when the receive data register full flag bit
(SSR:RDRF) is set to "1" and a reception error does not occur (SSR:PE, ORE, FRE=0).
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When the noise passes the filter, the incorrect data is received though the noise filter (where the serial
data input is sampled three times with the bus clock and decided by majority) is built in. As measures
against this, design the board so that the noise should not pass this filter or communicate so that noise
passing may not become a problem (for instance, when the error occurs due to adding the checksum of
data at the end, send it again).
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When any of following conditions is detected while receiving at the same time of or 1 to 2 bus clocks
before the sampling point for stop bit, its edge will be invalid and the next data may not be received
correctly. To output frames continuously, some space is required between the frames.
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Trailing edge of serial data (when ESCR:INV="0")
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Rising edge of serial data (when ESCR:INV="1")
MB91520 Series
MN705-00010-1v0-E
1465