XC68HC705F32 Motorola, XC68HC705F32 Datasheet - Page 112

• Manufacturer Part Number: XC68HC705F32
• Description: MICROCONTROLLER
• Manufacturer: Motorola

11.5
Functional description
A block diagram of the SCI is shown in
Figure
11-1. Option bits in serial control register1 (SCCR1)
select the ‘wake-up’ method (WAKE bit) and data word length (M bit) of the SCI. SCCR2 provides
control bits that individually enable the transmitter and receiver, enable system interrupts and
provide the wake-up enable bit (RWU) and the send break code bit (SBK). Control bits in the baud
rate register (BAUD) allow the user to select one of 32 different baud rates for the transmitter and
receiver (see
Section
11.11.5).
Data transmission is initiated by writing to the serial communications data register (SCDR).
Provided the transmitter is enabled, data stored in the SCDR is transferred to the transmit data
shift register. This transfer of data sets the transmit data register empty flag (TDRE) in the SCI
status register (SCSR) and generates an interrupt (if transmitter interrupts are enabled). The
transfer of data to the transmit data shift register is synchronized with the bit rate clock. All data is
transmitted least significant bit first. Upon completion of data transmission, the transmission
complete flag (TC) in the SCSR is set (provided no pending data, preamble or break is to be sent)
and an interrupt is generated (if the transmit complete interrupt is enabled). If the transmitter is
disabled, and the data, preamble or break (in the transmit data shift register) has been sent, the
TC bit will also be set. This will also generate an interrupt if the transmission complete interrupt
enable bit (TCIE) is set. If the transmitter is disabled during a transmission, the character being
transmitted will be completed before the transmitter gives up control of the TDO pin.
When SCDR is read, it contains the last data byte received, provided that the receiver is enabled.
The receive data register full flag bit (RDRF) in the SCSR is set to indicate that a data byte has
been transferred from the input serial shift register to the SCDR; this will cause an interrupt if the
receiver interrupt is enabled. The data transfer from the input serial shift register to the SCDR is
11
synchronized by the receiver bit rate clock. The OR (overrun), NF (noise), or FE (framing) error
flags in the SCSR may be set if data reception errors occurred.
An idle line interrupt is generated if the idle line interrupt is enabled and the IDLE bit (which detects
idle line transmission) in SCSR is set. This allows a receiver that is not in the wake-up mode to
detect the end of a message or the preamble of a new message, or to resynchronize with the
transmitter. A valid character must be received before the idle line condition or the IDLE bit will not
be set and idle line interrupt will not be generated.
TPG
MOTOROLA
SERIAL COMMUNICATIONS INTERFACE
MC68HC05F32
11-4