13.8 Idle-Line Multiprocessor Mode
In the idle-line multiprocessor protocol (ADDR/IDLE MODE bit=0), blocks are separated by having a longer idle
time between the blocks than between frames in the blocks. An idle time of ten or more high-level bits after a
frame indicates the start of a new block. The time of a single bit is calculated directly from the baud value (bits
per second). The idle-line multiprocessor communication format is shown in
is bit 3 of SCICCR).
Address
Data
Last Data
First frame within block
Is
address
; it follows idle
period of 10 bits or more
Frame within
block
Idle period
less than 10
bits
Idle period
of
10 bits
or more
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Several blocks of frames
Data format
(Pins SCIRXD, SCITXD)
Data format expanded
Idle periods of 10 bits or more
separate the blocks
Start
Start
Start
One block of frames
Figure 13-4. Idle-Line Multiprocessor Communication Format
13.8.1 Idle-Line Mode Steps
The steps followed by the idle-line mode:
1. SCI wakes up after receipt of the block-start signal.
2. The processor recognizes the next SCI interrupt.
3. The interrupt service routine compares the received address (sent by a remote transmitter) to its own.
4. If the CPU is being addressed, the service routine clears the SLEEP bit and receives the rest of the data
block.
5. If the CPU is not being addressed, the SLEEP bit remains set. This lets the CPU continue to execute its
main program without being interrupted by the SCI port until the next detection of a block start.
13.8.2 Block Start Signal
There are two ways to send a block-start signal:
•
Method 1:
Deliberately leave an idle time of ten bits or more by delaying the time between the transmission
of the last frame of data in the previous block and the transmission of the address frame of the new block.
•
Method 2:
The SCI port first sets the TXWAKE bit (SCICTL1, bit 3) to 1 before writing to the SCITXBUF
register. This sends an idle time of exactly 11 bits. In this method, the serial communications line is not idle
any longer than necessary. (A don't care byte has to be written to SCITXBUF after setting TXWAKE, and
before sending the address, so as to transmit the idle time.)
Serial Communications Interface (SCI)
SPRUH18I – JANUARY 2011 – REVISED JUNE 2022
TMS320x2806x Microcontrollers
805
Copyright © 2022 Texas Instruments Incorporated
Содержание TMS320 2806 Series
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