Analog Devices ADSP-BF506F Hardware Reference Manual page 1161

When the boot kernel is processing fill or initcode blocks it might require
extra processing time and needs to hold the host off from sending more
data. This is signalled with the
When equipped with a pull-up resistor the
behavior of an
the booting host. The host is not allowed to send data until
inactive after a reset cycle. Therefore a pulling resistor on the
is required.
If the resistor pulls to ground, the host must pause transmission when
is low and is permitted to send when
HWAIT
tor inverts the signal polarity of
transmitted byte.
During ADSP-BF50x boot operation, the host device more likely relies on
the output of UART0. Then, the use of
RTS
boot time the Blackfin processor does not evaluate
the host and the UART0
a high impedance state when the Blackfin processor is in reset or while
executing preboot, an external pull-up resistor to
Figure 24-19 and
mode. As soon as
receive a 0x40 byte for bit rate detection. After the bit rate is known, the
UART is enabled and the kernel transmits for bytes.
Figure 24-19 and
an extended initcode executes. Since code execution distracts from data
loading, the host device should be prevented from sending more data. The
timing is much more conservative than the
HWAIT
, the UART receive buffer may not be filled over watermark level
HWAIT
and might not be deasserted at all. If, however, the host relies on
UA0_RTS
, it will be stalled a couple of bytes later. Both methods are valid.
UA0_RTS
ADSP-BF50x Blackfin Processor Hardware Reference
HWAIT
output and could be connected to the
UA0_RTS
HWAIT
UA0_CTS
Figure 24-20 show the initial case of the UART boot
releases after reset, the boot kernel expects to
HWAIT
Figure 24-20 compare
System Reset and Booting
output as well as by the
signal imitates the
HWAIT
is high. A pull-up resis-
HWAIT
. The host should test
becomes optional. At
HWAIT
RTS
input is inactive. Since the
V
DDEXT
and
UA0_RTS
RTS
output.
RTS
input of
CTS
turns
HWAIT
signal
HWAIT
at every
HWAIT
signals driven by
is in
UA0_RTS
is recommended.
timing when
HWAIT
. If the host relies on
24-57