HC05 datasheet(105/232 Pages) MOTOROLA

105 / 232 page

MC68HC05X16

Rev. 1

MOTOROLA

7-3

SERIAL COMMUNICATIONS INTERFACE

7.2

SCI receiver features

•

Receiver wake-up function (idle line or address bit)

•

Idle line detection

•

Framing error detection

•

Noise detection

•

Overrun detection

•

Receiver data register full ﬂag

7.3

SCI transmitter features

•

Transmit data register empty ﬂag

•

Transmit complete ﬂag

•

Send break

7.4

Functional description

A block diagram of the SCI is shown in Figure 7-1. 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 7.11.5).

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 (see

Figure 7-2). 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.

103

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