13.9 Address-Bit Multiprocessor Mode
In the address-bit protocol (ADDR/IDLE MODE bit=1), frames have an extra bit called an address bit that
immediately follows the last data bit. The address bit is set to 1 in the first frame of the block and to 0 in all other
frames. The idle period timing is irrelevant (see
13.9.1 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.
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
Figure 13-6. Address-Bit Multiprocessor Communication Format
Serial Communications Interface (SCI)
SPRUH18I – JANUARY 2011 – REVISED JUNE 2022
TMS320x2806x Microcontrollers
807
Copyright © 2022 Texas Instruments Incorporated
Содержание TMS320 2806 Series
Страница 2: ......