AT89C5122 ATMEL [ATMEL Corporation], AT89C5122 Datasheet - Page 75

• Manufacturer Part Number: AT89C5122
• Description: MICROCONTROLLER WITH USB AND SMART CARD READER INTERFACES
• Manufacturer: ATMEL [ATMEL Corporation]

Transmit / Receive Buffer
4202D–SCR–06/05
The contents of the SCIBUF Transmit / Receive Buffer is transferred or received into /
from the Shift Register. The Shift Register is not accessible by microcontroller. Its role is
to prepare the byte to be copied on the I/O pin for a transmission or in the SCIBUF
buffer after a reception.
During a character transmission process, as soon as the contents of the SCIBUF buffer
is transferred to the shift register, the SCTBE bit is set in SCISR register to indicate that
the SCIBUF buffer is empty and ready to accept a new byte. This mechanism avoids to
wait for the complete transmission of the previous byte before writing a new byte in the
buffer and enables to speed up the transmission.
During a character reception process, the contents of the Shift Register is transferred in
the SCIBUF buffer.
Warning : the SCTBI, SCTI SCRI and SCPI bits have the same function as SCTBE,
SCTC, SCRC and SCPE bits. The first ones are able to generate interruptions if the
interruptions are enabled in SCIER register while the second ones are only status bits to
be used in pulling mode. If the interruption mode is not used, the status bits must be
used. The SCTBI, SCTI and SCRI bits do not contain valid information while their
respective interrupt enable bits ESCTBI, EXCTI, ESCRI are cleared.
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If the Character repetition mode is not selected (bit CREP=0 in SCICR), as
soon as the contents of the Shift Register is transferred to I/O pin, the SCTC
bit is set in SCISR register to indicate that the byte has been transmitted.
If the Character repetition mode is selected (bit CREP=1 in SCICR) The
TERMINAL will be able to repeat characters as requested by the ICC (See
the Parity Error in T=0 protocol description in the definition paragraph
above). The SCTC bit in SCISR register will be set after a successful
transmission (no retry or no further retry requested by the ICC). If the
number of retries is exhausted (up to 4 retries depending on CREPSEL bit in
SCSR) and the last retry is still unsuccessful, the SCTC bit in SCISR will not
be set and the SCPE bit in SCISR register will be set instead.
If the Character repetition mode is not selected (bit CREP=0 in SCICR), as
soon as the contents of the Shift Register is transferred to the SCIBUF the
SCRC bit is set in SCISR register to indicate that the byte has been
received, and the SCIBUF contains a valid character ready to be red by the
microcontroller.
If the Character repetition mode is selected (bit CREP=1 in SCICR) The
TERMINAL will be able to request repetition if the received character exhibit
a parity error. Up to 4 retries can be requested depending on CREPSEL bit
in SCSR. The SCRC bit will be set in SCISR register after a successful
reception, first reception or after retry(ies). If the number of retries is
exhausted (up to 4 retries depending on CREPSEL bit in SCSR) and the last
retry is still unsuccessful, the SCRC bit and the SCPE bit in SCISR register
will be set. It will be possible to read the erroneous character.
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