mc68hc08az60 Freescale Semiconductor, Inc, mc68hc08az60 Datasheet - Page 185

• Manufacturer Part Number: mc68hc08az60
• Description: M68hc08 Family Of 8-bit Microcontroller Units Mcus
• Manufacturer: Freescale Semiconductor, Inc

Character Length
Character
R eception
Data Sampling
13-sci
MOTOROLA
The receiver can accommodate either 8-bit or 9-bit data. The state of the
M bit in SCI control register 1 (SCC1) determines character length.
When receiving 9-bit data, bit R8 in SCI control register 2 (SCC2) is the
ninth bit (bit 8). When receiving 8-bit data, bit R8 is a copy of the eighth
bit (bit 7).
During an SCI reception, the receive shift register shifts characters in
from the RxD pin. The SCI data register (SCDR) is the read-only buffer
between the internal data bus and the receive shift register.
After a complete character shifts into the receive shift register, the data
portion of the character transfers to the SCDR. The SCI receiver full bit,
SCRF, in SCI status register 1 (SCS1) becomes set, indicating that the
received byte can be read. If the SCI receive interrupt enable bit, SCRIE,
in SCC2 is also set, the SCRF bit generates a receiver CPU interrupt
request.
The receiver samples the RxD pin at the RT clock rate. The RT clock is
an internal signal with a frequency 16 times the baud rate. To adjust for
baud rate mismatch, the RT clock is resynchronized at the following
times (see
To locate the start bit, data recovery logic does an asynchronous search
for a logic 0 preceded by three logic 1s. When the falling edge of a
possible start bit occurs, the RT clock begins to count to 16.
Freescale Semiconductor, Inc.
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Serial Communications Interface Module (SCI)
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After every start bit
After the receiver detects a data bit change from logic 1 to logic 0
(after the majority of data bit samples at RT8, RT9, and RT10
returns a valid logic 1 and the majority of the next RT8, RT9, and
RT10 samples returns a valid logic 0)
Figure
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8):
Serial Communications Interface Module (SCI)
MC68HC08AZ60 — Rev 1.0
Functional Description
185