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13.7 SCI Multiprocessor Communication
The multiprocessor communication format allows one processor to efficiently send blocks of data to other
processors on the same serial link. On one serial line, there should be only one transfer at a time. In other
words, there can be only one talker on a serial line at a time.
Address Byte
The first byte of a block of information that the talker sends contains an address byte that is read by all listeners.
Only listeners with the correct address can be interrupted by the data bytes that follow the address byte. The
listeners with an incorrect address remain uninterrupted until the next address byte.
Sleep Bit
All processors on the serial link set the SCI SLEEP bit (bit 2 of SCICTL1) to 1 so that they are interrupted
only when the address byte is detected. When a processor reads a block address that corresponds to the CPU
device address as set by your application software, your program must clear the SLEEP bit to enable the SCI to
generate an interrupt on receipt of each data byte.
Although the receiver still operates when the SLEEP bit is 1, it does not set RXRDY, RXINT, or any of the
receiver error status bits to 1 unless the address byte is detected and the address bit in the received frame is a 1
(applicable to address-bit mode). The SCI does not alter the SLEEP bit; your software must alter the SLEEP bit.
13.7.1 Recognizing the Address Byte
A processor recognizes an address byte differently, depending on the multiprocessor mode used. For example:
• The idle-line mode (
) leaves a quiet space before the address byte. This mode does not have an
extra address/data bit and is more efficient than the address-bit mode for handling blocks that contain more
than ten bytes of data. The idle-line mode should be used for typical non-multiprocessor SCI communication.
) adds an extra bit (that is, an address bit) into every byte to distinguish
addresses from data. This mode is more efficient in handling many small blocks of data because, unlike the
idle mode, it does not have to wait between blocks of data. However, at a high transmit speed, the program is
not fast enough to avoid a 10-bit idle in the transmission stream.
13.7.2 Controlling the SCI TX and RX Features
The multiprocessor mode is software selectable via the ADDR/IDLE MODE bit (SCICCR, bit 3). Both modes use
the TXWAKE flag bit (SCICTL1, bit 3), RXWAKE flag bit (SCIRXST, bit1), and the SLEEP flag bit (SCICTL1, bit
2) to control the SCI transmitter and receiver features of these modes.
13.7.3 Receipt Sequence
In both multiprocessor modes, the receive sequence is as follows:
1. At the receipt of an address block, the SCI port wakes up and requests an interrupt (bit number 1 RX/BK
INT ENA-of SCICTL2 must be enabled to request an interrupt). It reads the first frame of the block, which
contains the destination address.
2. A software routine is entered through the interrupt and checks the incoming address. This address byte is
checked against its device address byte stored in memory.
3. If the check shows that the block is addressed to the device CPU, the CPU clears the SLEEP bit and reads
the rest of the block. If not, the software routine exits with the SLEEP bit still set, and does not receive
interrupts until the next block start.
Serial Communications Interface (SCI)
804
TMS320x2806x Microcontrollers
SPRUH18I – JANUARY 2011 – REVISED JUNE 2022
Copyright © 2022 Texas Instruments Incorporated
Содержание TMS320 2806 Series
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