SCI_Boot
Enable the SCI-A clock
set the LSPCLK to /4
functionality and pullups on
Enable the SCIA TX and RX pin
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
Autobaud
lock
?
No
Yes
Echo autobaud character
Read KeyValue
Yes
No
Valid
KeyValue
(0x08AA)
?
Jump to Flash
Read and discard 8
reserved words
Read EntryPoint address
Call CopyData
EntryPoint
Return
Set GetWord function pointer
to SCIA_GetWordData
TX and RX
C-Boot ROM Description
645
SPRUHE8E – October 2012 – Revised November 2019
Copyright © 2012–2019, Texas Instruments Incorporated
ROM Code and Peripheral Booting
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.
Figure 6-18. Overview of SCI_Boot Function