Maxim Integrated Secure Microcontroller - Manual (Page 142)

Secure Microcontroller User’s Guide
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16.6 Auto-Baud Rate Detection
The serial bootstrap loader can automatically detect, within certain limits, the external baud rate and
configure itself to that speed. When the serial bootstrap loader mode is first invoked, the device will
watch for a character on the serial port. If received at one of the supported baud rates, then the
serial program load mode will be established. The loader expects to talk asynchronously at 300, 1200,
2400, 9600, 19200, or 57600 baud using eight data bits, no parity, and one stop bit in full duplex. A break
signal followed by a carriage return forces the loader to auto-baud again. Although an 11.0592 MHz
crystal is standard for generating baud rates, the auto-baud rate detector allows a variety of crystals to be
used. If a crystal frequency other than 11.0592MHz is used, the baud rate frequencies that are recognized
by the serial loader are shown in
Table 16-A . Other crystals generate nonstandard baud rates.
Table 16-A. Serial Loader Baud Rates For Different Crystal Frequencies
SECURE MICROCONTROLLER
CRYSTAL FREQUENCY (MHz)
BAUD RATE
300 1200 2400 9600 19200 57600
14.7456 Y Y Y Y
11.0592 Y Y Y Y Y Y
9.21600 Y Y Y Y
7.37280 Y Y Y Y
5.52960 Y Y Y Y
1.84320 Y Y Y Y
16.7 Bootstrap Loader Initialization
When loader mode is invoked, the device will await an incoming character at a valid baud rate
through either the serial port (in Serial Program Load mode) or via the parallel interface (in Parallel
Program Load mode). At this point, the bootstrap loader transmits a banner, similar to the one shown
below, to the host to indicate that it has been invoked. The banner will be followed by a “>” prompt
which indicates the device is ready to receive a command.
DS500X LOADER VERSION X.X COPYRIGHT © XXX DALLAS SEMICONDUCTOR
>