Figure 4-5 illustrates an example of transmitter signal timing that assumes the following conditions:
- Address-bit wake-up mode (address bit does not appear in idle-line mode)
- Three bits per character
Notes:
- Bit TXENA (SCICTL1, bit 1)
goes high, enabling the transmitter to send data.
- SCITXBUF is written to; thus,
(1) the transmitter is no longer empty, and (2) TXRDY goes low.
- The SCI transfers data to the
shift register (TXSHF). The transmitter is ready for a second character
(TXRDY goes high), and the transmitter requests an interrupt (to enable an
interrupt, bit TX INT ENA — SCICTL2, bit 0 — must be set).
- 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.)
- Transmission of the first
character is complete. Transfer of the second character to shift register
TXSHF begins.
- Bit TXENA goes low to disable
the transmitter; the SCI finishes transmitting the current character.
- Transmission of the second
character is complete; transmitter is empty and ready for new
character.