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No
Reached
maximum
retries?
Yes
Report a
timeout error
Fetch Response
Send 0x00 to
No
shift out 1 byte
from target
Reached
No
maximum
retries?
Send 0x00 to
shift out 1 byte
from target
Yes
Report a timeout
error (End)
No
Figure 13-21. Host reads response from target via SPI
13.4.3 USB peripheral
The Kinetis Bootloader in the ROM supports loading data into flash via the USB
peripheral. The target is implemented as a USB HID class.
Freescale Semiconductor, Inc.
Fetch ACK
Send 0x00 to
shift out 1 byte
from target
No
0x5A
received?
Next action
Figure 13-20. Host reads ACK from target via SPI
0x5A
received?
Yes
Write 0x00s to shift
out payload length
0xA4
Yes
received?
part from target
(2 bytes)
KL27 Sub-Family Reference Manual , Rev. 5, 01/2016
Chapter 13 Kinetis ROM Bootloader
Process NAK
Send 0x00 to
Yes
shift out 1 byte
from target
Yes
End
Write 0x00s to shift
out payload data
from target
Yes
Payload length
less than supported
length?
Write 0x00s to shift
out CRC checksum
from target
(2 bytes)
Report an error
No
0xA2
Yes
received?
No
No
0xA1
received?
Set payload length
No
to maximum
supported length
213
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