13.8.3 Wake-UP Temporary (WUT) Flag
Associated with the TXWAKE bit is the wake-up temporary (WUT) flag. WUT is an internal flag, double-buffered
with TXWAKE. When TXSHF is loaded from SCITXBUF, WUT is loaded from TXWAKE, and the TXWAKE bit is
cleared to 0. This arrangement is shown in
TXWAKE
WUT
Transmit buffer (SCITXBUF)
TXSHF
1
8
Figure 13-5. Double-Buffered WUT and TXSHF
13.8.3.1 Sending a Block Start Signal
To send out a block-start signal of exactly one frame time during a sequence of block transmissions:
1. Write a 1 to the TXWAKE bit.
2. Write a data word (content not important: a don’t care) to the SCITXBUF register (transmit data buffer) to
send a block-start signal. (The first data word written is suppressed while the block-start signal is sent out
and ignored after that.) When the TXSHF (transmit shift register) is free again, SCITXBUF contents are
shifted to TXSHF, the TXWAKE value is shifted to WUT, and then TXWAKE is cleared.
Because TXWAKE was set to a 1, the start, data, and parity bits are replaced by an idle period of 11 bits
transmitted following the last stop bit of the previous frame.
3. Write a new address value to SCITXBUF.
A don’t-care data word must first be written to register SCITXBUF so that the TXWAKE bit value can
be shifted to WUT. After the don’t-care data word is shifted to the TXSHF register, the SCITXBUF (and
TXWAKE, if necessary) can be written to again because TXSHF and WUT are both double-buffered.
13.8.4 Receiver Operation
The receiver operates regardless of the SLEEP bit. However, the receiver neither sets RXRDY nor the error
status bits, nor does it request a receive interrupt until an address frame is detected.
Serial Communications Interface (SCI)
806
TMS320x2806x Microcontrollers
SPRUH18I – JANUARY 2011 – REVISED JUNE 2022
Copyright © 2022 Texas Instruments Incorporated
Summary of Contents for TMS320 2806 Series
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