Rabbit 6000 User’s Manual
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Note that the processor can be told to re-enter bootstrap mode at any time by setting bit 7 of SPCR low;
once this occurs and the least significant four bits of the current PC address are zero, the processor will
sample the state of the SMODE pins and respond accordingly. This feature allows in-line downloading
from the selected bootstrap port; once the download is complete, bit 7 of SPCR can be set high and the
processor will continue operating from where it left off.
As a security feature, any attempt to enter the bootstrap mode from either the SMODE pins or by writing
to bit 7 of the SPCR will erase the data stored in the onchip-encryption RAM. This prevents loading a
small program in memory to read out the data.
3.3.1 Asynchronous Serial Bootstrap
When the
asynchronous serial bootstrap mode
is selected by the SMODE pins, the Rabbit 6000 will begin
accepting triplets at 2400 bps on Serial Port A. The baud rate is generated from the 32 kHz clock input, so
a 32 kHz clock is required for this mode.
3.3.2 Serial Flash Bootstrap
When the
serial flash bootstrap mode
is selected by the SMODE pins, the Rabbit 6000 will enable the SPI
serial flash bootstrap port on pins PD4, PD5, PD6, and PB0; the pins’ functionality is listed in Table 3-3
below. Note that these pins can be used for Serial Port B in normal operation, so the serial flash may be
accessed with that serial port during normal operation.
The Rabbit 6000 divides the main clock by 64 to provide the SPI clock for the serial flash bootstrap. Once
this mode is entered, the Rabbit 6000 will send the byte sequence “0x03 0x00 0x00 0x00”, which is an
industry-standard command that enables continuous read mode starting at serial flash address 0x0.
Figure 3.1 provides a sample timing diagram. The Rabbit 6000 will then read triplets out of the serial flash
until the bootstrap mode is exited.
Figure 3.1 SPI Timing Diagram for Serial Flash Bootstrap Mode
Table 3-3. Serial Flash Bootstrap Pin Functions
Pin
SPI Signal
Operation
PD4
MOSI
Rabbit data transmit (to serial flash)
PD5
MISO
Rabbit data receive (from serial flash)
PD6
CS
Chip select (to serial flash)
PB0
SCK
Serial clock (output to serial flash)
Summary of Contents for 6000
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