MSB
Parity
0
1
Addr
Data
Addr
ÉÉ
ÉÉ
ÉÉ
ÉÉ
ÉÉ
ÉÉ
ÉÉ
ÉÉ
Data format
(Pins SCIRXD, SCITXD)
Data format expanded
First frame within
block is address
(Address bit is 1)
1
ÉÉ
ÉÉ
ÉÉ
ÉÉ
ÉÉÉ
ÉÉÉ
ÉÉÉ
ÉÉÉ
ÉÉÉ
ÉÉÉ
ÉÉÉ
ÉÉÉ
ÉÉ
ÉÉ
ÉÉ
ÉÉ
ÉÉÉ
ÉÉÉ
ÉÉÉ
ÉÉÉ
ÉÉÉ
ÉÉÉ
ÉÉÉ
ÉÉÉ
Idle time is of
no significance
Next frame is address
for next block
(Address bit is 1)
Start
LSB
Stop
Address-bit mode frame example
Address bit
Frame within block
(Address bit is 0)
1
Start
Start
Start
One block
Idle periods of no significance
Blocks of frames
Enhanced SCI Module Overview
987
SPRUH22I – April 2012 – Revised November 2019
Copyright © 2012–2019, Texas Instruments Incorporated
C28 Serial Communications Interface (SCI)
13.1.1.6.1 Sending an Address
The TXWAKE bit value is placed in the address bit. During transmission, when the SCITXBUF register
and TXWAKE are loaded into the TXSHF register and WUT respectively, TXWAKE is reset to 0 and WUT
becomes the value of the address bit of the current frame. Thus, to send an address:
1. Set the TXWAKE bit to 1 and write the appropriate address value to the SCITXBUF register.
When this address value is transferred to the TXSHF register and shifted out, its address bit is sent as
a 1. This flags the other processors on the serial link to read the address.
2. Write to SCITXBUF and TXWAKE after TXSHF and WUT are loaded. (Can be written to immediately
since both TXSHF and WUT are both double-buffered.
3. Leave the TXWAKE bit set to 0 to transmit non-address frames in the block.
NOTE:
As a general rule, the address-bit format is typically used for data frames of 11 bytes or less.
This format adds one bit value (1 for an address frame, 0 for a data frame) to all data bytes
transmitted. The idle-line format is typically used for data frames of 12 bytes or more.
Figure 13-6. Address-Bit Multiprocessor Communication Format
13.1.1.7 SCI Communication Format
The SCI asynchronous communication format uses either single line (one way) or two line (two way)
communications. In this mode, the frame consists of a start bit, one to eight data bits, an optional
even/odd parity bit, and one or two stop bits (shown in
). There are eight SCICLK periods per
data bit.
The receiver begins operation on receipt of a valid start bit. A valid start bit is identified by four
consecutive internal SCICLK periods of zero bits as shown in
. If any bit is not zero, then the
processor starts over and begins looking for another start bit.
For the bits following the start bit, the processor determines the bit value by making three samples in the
middle of the bits. These samples occur on the fourth, fifth, and sixth SCICLK periods, and bit-value
determination is on a majority (two out of three) basis.
illustrates the asynchronous
communication format for this with a start bit showing where a majority vote is taken.