Datasheet

680
32133D–11/2011
UC3D
Where is the baud rate frequency and is the frequency of the internal RC120M. TUNE is
the value returned by the BAUD_RATE response.
To find the max frequency the user can issue the TUNE command to the AW to make it return
the TUNE value. This value can be used to compute the . The maximum operational fre-
quency ( ) is then:
31.4.6.8 Service Access Bus
The AVR32 architecture offers a common interface for access to On-Chip Debug, programming,
and test functions. These are mapped on a common bus called the Service Access Bus (SAB),
which is linked to the aWire through a bus master module, which also handles synchronization
between the aWire and SAB clocks.
For more information about the SAB and a list of SAB slaves see the Service Access Bus
chapter.
SAB Clock
When accessing the SAB through the aWire there are no limitations on baud rate frequency
compared to chip frequency, although there must be an active system clock in order for the SAB
accesses to complete. If the system clock (CLK_SYS) is switched off in sleep mode, activity on
the aWire pin will restart the CLK_SYS automatically, without waking the device from sleep.
aWire masters may optimize the transfer rate by adjusting the baud rate frequency in relation to
the CLK_SYS. This ratio can be measured with the MEMORY_SPEED_REQUEST command.
When issuing the MEMORY_SPEED_REQUEST command a counter value CV is returned. CV
can be used to calculate the SAB speed ( ) using this formula:
SAB Address Mode
The Service Access Bus uses 36 address bits to address memory or registers in any of the
slaves on the bus. The bus supports sized accesses of bytes (8 bits), halfwords (16 bits), or
words (32 bits). All accesses must be aligned to the size of the access, i.e. halfword accesses
must have the lowest address bit cleared, and word accesses must have the two lowest address
bits cleared.
Two instructions exist to access the SAB: MEMORY_WRITE and MEMORY_READ. These two
instructions write and read words, halfwords, and bytes from the SAB.
Busy Reporting
If the aWire master, during a MEMORY_WRITE or a MEMORY_READ command, transmit
another byte when the aWire is still busy sending the previous byte to the SAB, the AW will
respond with a MEMORY_READ_WRITE_STATUS error. See chapter Section 31.4.8.5 for
more details.
f
aw
TUNE f×
br
8
-----------------------------=
f
br
f
aw
f
aw
f
brmax
f
brmax
f
aw
4
-------=
f
sab
f
sab
3f
aw
CV 3–
-----------------=