Serial Communications Interface (SCI)
Registers
MC68HC(7)05H12
—
Rev. 1.0
General Release Specification
MOTOROLA
Serial Communications Interface (SCI)
139
L
G
R
TDRE — Transmit Data Register Empty Flag
This bit is set when the byte in the transmit data register is transferred
to the serial shift register. New data will not be transmitted unless the
SCSR register is read before writing to the transmit data register.
Reset sets this bit.
TC — Transmit Complete Flag
This bit is set to indicate that the SCI transmitter has no meaningful
information to transmit (no data in shift register, no preamble, no
break). When TC is set the serial line will go idle (continuous MARK).
Reset sets this bit.
RDRF -— Receive Data Register Full Flag
This bit is set when the contents of the receiver serial shift register is
transferred to the receiver data register.
IDLE — Idle Line Detected Flag
This bit is set when a receiver idle line is detected (the receipt of a
minimum of ten/eleven consecutive ‘1’s). This bit will not be set by the
idle line condition when the RWU bit is set. Once cleared, IDLE will
not be set again until after RDRF has been set, (until after the line has
been active and becomes idle again).
OR — Overrun Error Flag
This bit is set when a new byte is ready to be transferred from the
receiver shift register to the receiver data register and the receive data
register is already full (RDRF bit is set). Data transfer is inhibited until
this bit is cleared.
NF — Noise Error Flag
This bit is set if there is noise on a “valid” start bit, any of the data bits,
or on the stop bit. The NF bit is set during the same cycle as the RDRF
bit but does not get set in the case of an overrun (OR).
FE — Framing Error Flag
This bit is set when the word boundaries in the bit stream are not
synchronized with the receiver bit counter (generated by the reception
of a logic zero bit where a stop bit was expected). The FE bit reflects
the status of the byte in the receive data register and the transfer from