MC68332ACFC25 Freescale Semiconductor, MC68332ACFC25 Datasheet - Page 151

• Manufacturer Part Number: MC68332ACFC25
• Description: IC MCU 32BIT 25MHZ 132-PQFP
• Manufacturer: Freescale Semiconductor
• Series: M683xxr

Specifications of MC68332ACFC25

• Core Processor: CPU32
• Core Size: 32-Bit
• Speed: 25MHz
• Connectivity: EBI/EMI, SCI, SPI, UART/USART
• Peripherals: POR, PWM, WDT
• Number Of I /o: 15
• Program Memory Type: ROMless
• Ram Size: 2K x 8
• Voltage - Supply (vcc/vdd): 4.5 V ~ 5.5 V
• Oscillator Type: Internal
• Operating Temperature: -40°C ~ 85°C
• Package / Case: 132-QFP
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Eeprom Size: -
• Program Memory Size: -
• Data Converters: -

6.4.3.7 Idle-Line Detection
MC68332
USER’S MANUAL
Receiver bit processor logic drives a state machine that determines the logic level for
each bit-time. This state machine controls when the bit processor logic is to sample
the RXD pin and also controls when data is to be passed to the receive serial shifter.
A receive time (RT) clock is used to control sampling and synchronization. Data is
shifted into the receive serial shifter according to the most recent synchronization of
the RT clock with the incoming data stream. From this point on, data movement is syn-
chronized with the MCU system clock. Operation of the receiver state machine is de-
tailed in the QSM Reference Manual (QSMRM/AD).
The number of bits shifted in by the receiver depends on the serial format. However,
all frames must end with at least one stop bit. When the stop bit is received, the frame
is considered to be complete, and the received data in the serial shifter is transferred
to the RDR. The receiver data register flag (RDRF) is set when the data is transferred.
Noise errors, parity errors, and framing errors can be detected while a data stream is
being received. Although error conditions are detected as bits are received, the noise
flag (NF), the parity flag (PF), and the framing error (FE) flag in SCSR are not set until
data is transferred from the serial shifter to RDR.
RDRF must be cleared before the next transfer from the shifter can take place. If
RDRF is set when the shifter is full, transfers are inhibited and the overrun error (OR)
flag in the SCSR is set. OR indicates that the CPU needs to service RDR faster. When
OR is set, the data in RDR is preserved, but the data in the serial shifter is lost. Be-
cause framing, noise, and parity errors are detected while data is in the serial shifter,
FE, NF, and PF cannot occur at the same time as OR.
When the CPU reads the SCSR and the SCDR in sequence, it acquires status and
data, and also clears the status flags. Reading the SCSR acquires status and arms
the clearing mechanism. Reading the SCDR acquires data and clears the SCSR.
When RIE in SCCR1 is set, an interrupt request is generated whenever RDRF is set.
Because receiver status flags are set at the same time as RDRF, they do not have
separate interrupt enables.
During a typical serial transmission, frames are transmitted isochronously and no idle
time occurs between frames. Even when all the data bits in a frame are logic ones, the
start bit provides one logic zero bit-time during the frame. An idle line is a sequence of
contiguous ones equal to the current frame size. Frame size is determined by the state
of the M bit in SCCR1.
The SCI receiver has both short and long idle-line detection capability. Idle-line detec-
tion is always enabled. The idle line type (ILT) bit in SCCR1 determines which type of
detection is used. When an idle line condition is detected, the IDLE flag in SCSR is set.
For short idle-line detection, the receiver bit processor counts contiguous logic one bit-
times whenever they occur. Short detection provides the earliest possible recognition
of an idle line condition, because the stop bit and contiguous logic ones before and
after it are counted. For long idle-line detection, the receiver counts logic ones after
the stop bit is received. Only a complete idle frame causes the IDLE flag to be set.
Freescale Semiconductor, Inc.
For More Information On This Product,
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Go to: www.freescale.com
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