Overview Of Sci_Boot Function - Texas Instruments Concerto F28M35 Series Technical Reference Manual

C-Boot ROM Description
The device communicates with the external host device by communication through the SCI-A peripheral.
The autobaud feature of the SCI port is used to lock baud rates with the host. For this reason the SCI
loader is very flexible and you can use a number of different baud rates to communicate with the device.
After each data transfer, the 28x will echo back the 8-bit character received to the host. In this manner, the
host can perform checks that each character was received by the 28x.
At higher baud rates, the slew rate of the incoming data bits can be effected by transceiver and connector
performance. While normal serial communications may work well, this slew rate may limit reliable auto-
baud detection at higher baud rates (typically beyond 100kbaud) and cause the auto-baud lock feature to
fail. To avoid this, the following is recommended:
1. Achieve a baud-lock between the host and 28x SCI bootloader using a lower baud rate.
2. Load the incoming 28x application or custom loader at this lower baud rate.
3. The host may then handshake with the loaded 28x application to set the SCI baud rate register to the
desired high baud rate.
SCI_Boot
Set GetWord function pointer
to SCIA_GetWordData
Enable the SCI-A clock
set the LSPCLK to /4
Enable the SCIA TX and RX pin
functionality and pullups on
TX and RX
Setup SCI-A for
1 stop, 8-bit character,
no parity, use internal
SC clock, no loopback,
disable Rx/Tx interrupts
Disable SCI FIFOs
Prime SCI-A baud register
Enable autobaud detection
No
Autobaud
lock
?
602
ROM Code and Peripheral Booting
Figure 6-19. Overview of SCI_Boot Function
Yes
Copyright © 2012–2019, Texas Instruments Incorporated
Echo autobaud character
Read KeyValue
Valid
No
KeyValue
(0x08AA)
?
Yes
Read and discard 8
reserved words
Read EntryPoint address
Call CopyData
Return
EntryPoint
SPRUH22I – April 2012 – Revised November 2019
www.ti.com
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