DSP
SCIRXDA
SCITXDA
Host
(Data and program
source)
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Bootloader Features
189
SPRUI07–March 2020
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Boot ROM
Table 2-8. McBSP 16-Bit Data Stream (continued)
Word Contents Description
. XXXX Last word of the first block of the source being loaded
. MMNN Block size of the 2nd block to load = 0xMMNN words
. AABB Destination address of second block Addr[31:16]
. CCDD Destination address of second block Addr[15:0]
. XXXX First word of the second block in the source being loaded
. …
n XXXX Last word of the last block of the source being loaded
n+1 0000 Block size of 0000h - indicates end of the source program
2.2.17 SCI_Boot Function
The SCI boot mode asynchronously transfers code from SCI-A to internal memory. This boot mode only
supports an incoming 8-bit data stream and follows the same data flow as outlined in Example 2-4.
Figure 2-15. Overview of SCI Bootloader Operation
The SCI-A loader uses following pins:
• SCIRXDA on GPIO28
• SCITXDA on GPIO29
The 28x device communicates with the external host device 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 affected 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.