Datasheet

677
32133D–11/2011
UC3D
31.4.5.1 I/O Lines
The pin used by AW is multiplexed with the RESET_N pin. The reset functionality is the default
function of this pin. To enable the aWire functionality on the RESET_N pin the user must enable
the AW either by sending the enable sequence over the RESET_N pin from an external aWire
master or by enabling the aWire user interface.
In 2-pin mode data is received on the RESET_N line, but transmitted on the DATAOUT line.
After sending the 2_PIN_MODE command the DATAOUT line is automatically enabled. All other
peripheral functions on this pin is disabled.
31.4.5.2 Power Management
When debugging through AW the system clocks are automatically turned on to allow debugging
in sleep modes.
31.4.5.3 Clocks
The aWire UART uses the internal 120 MHz RC oscillator (RC120M) as clock source for its
operation. When enabling the AW the RC120M is automatically started.
31.4.6 Functional Description
31.4.6.1 aWire Communication Protocol
The AW is accessed through the RESET_N pin shown in Table 31-6 on page 676. The AW com-
municates through a UART operating at variable baud rate (depending on a sync pattern) with
one start bit, 8 data bits (LSB first), one stop bit, and no parity bits. The aWire protocol is based
upon command packets from an externalmaster and response packets from the slave (AW). The
master always initiates communication and decides the baud rate.
The packet contains a sync byte (0x55), a command/response byte, two length bytes (optional),
a number of data bytes as defined in the length field (optional), and two CRC bytes. If the com-
mand/response has the most significant bit set, the command/response also carries the optional
length and data fields. The CRC field is not checked if the CRC value transmitted is 0x0000.
CRC calculation
Table 31-7.
aWire Packet Format
Field Number of bytes Description Comment Optional
SYNC 1 Sync pattern (0x55).
Used by the receiver to set the baud rate
clock.
No
COMMAND/
RESPONSE
1
Command from the master or
response from the slave.
When the most significant bit is set the
command/response has a length field. A
response has the next most significant bit
set. A command does not have this bit set.
No
LENGTH 2
The number of bytes in the DATA
field.
Yes
DATA LENGTH
Data according to command/
response.
Yes
CRC 2
CRC calculated with the FCS16
polynomial.
CRC value of 0x0000 makes the aWire
disregard the CRC if the master does not
support it.
No