Specifications

SCI Communication Format
8-16
Figure 8–8. SCI TX Signals in Communications Modes
Ad
TXENA
SCITXD pin
16
34
5
2
012 012
TXRDY
TX EMPTY
7
Start
Start StopStopAd PaPa
First Character
Second Character
Frame
Frame
Notes: 1) Bit TXENA (SCICTL1.1) goes high, enabling the transmitter to send data.
2) SCITXBUF is written to; thus, (1) the transmitter is no longer empty, and (2) TXRDY goes low.
3) The SCI transfers data to the shift register (TXSHF). The transmitter is ready for a second character (TXRDY goes
high), and it requests an interrupt (to enable an interrupt, bit TX INT ENA — SCICTL2.0 — must be set).
4) The program writes a second character to SCITXBUF after TXRDY goes high (item 3). (TXRDY goes low again after
the second character is written to SCITXBUF.)
5) Transmission of the first character is complete. TX EMPTY goes high temporarily. Transfer of the second character
to shift register TXSHF begins.
6) Bit TXENA goes low to disable the transmitter; the SCI finishes transmitting the current character.
7) Transmission of the second character is complete; transmitter is empty and ready for new character.