User manual

50
Serial BUS Analysis
Read address: Yellow
Write address: Magenta
Data: Cyan
Start: White
Stop: White
No acknowledge: Red
Acknowledge: Green
12.4.2 I
2
C BUS Triggering
After the BUSconguration,itwillbepossibletotrigger
on various events. Press the TYPE button in the TRIGGER
section and choose the soft menu key SERIAL BUSES.
Then press the SOURCE button in the TRIGGER section
and choose I
2
C Bus. This will only be available if it was
conguredearlier.PresstheFILTERbuttonintheTRIGGER
section to list all available I
2
C trigger conditions.
Following triggerconditionscanbedened:
START: The oscilloscope triggers on the frame start
sequence.The start sequence is the falling slope on SDA
when SCL is high.
STOP: The oscilloscope triggers on the frame stop
sequence. The start signal is the rising slope on SDA
when SCL is high.
RESTART: The oscilloscope triggers, if a new start
sequence occurs before the stop condition. The new start
signal is a repeated start signal.
NOT-ACKNOWLEDGE: The NOT-ACKNOWLEDGE bit is
the 9th bit in a data or address unit of the SDA line. For
NOT-ACKNOWLEDGE, the Acknowledge bit is on SDA
high, although it should be low.
READ/WRITE: The soft menu key READ/WRITE offers
additional trigger options. You can use the soft menu key
MASTER to toggle the trigger condition between read and
writeaccess.The8thbitoftherstdataunit(depending
on the address length) is used to distinguish between
read and write access. The selected condition is displayed
in the I
2
C settings window and is highlighted by the menu
key in blue. Theaddresslength(inbit)denesthe
maximum number of slave addresses to be used with the
bus. For a 7 bit address length, the maximum number of
The address decoding is a 7-bit value. The 8th bit of write-read is
decoded in color, not in the HEX value of the address.
available addresses is 112. The 10 bit addressing mode is
downward compatible with the 7 bit addressing mode by
using 4 of 16 reserved addresses and can be used
simultaneously. For a 10 bit address length, a total of
1136 addresses (1024 + 128 - 16) is available. The highest
10 bit address is 1023 (0x3FF). The selected address
length is displayed in the I
2
C settings window and is high-
lighted by the menu key in blue. The SLAVE ADDRESS is
the address used on the BUS to distinguish which slave
the master communicates with. Use the universal knob in
the CURSOR/MENU section to select the address for the
observing bus participant to be triggered. The soft menu
DATAenablesyoutoenterspecicdatainadditiontothe
address. With this menu, you can trigger on clearly
deneddatabytes(colorcyan)withinthetransmission,
allowingyoutolteroutirrelevanttransmissions.Youcan
trigger on up to 24 bit (3 byte) of data. An offset of 0 to
4095 to the address is allowed. Select BYTE OFFSET
whichdenesthedistancebetweenthebytesrelevant
for the trigger condition and the address. In most cases,
the byte offset is zero if the trigger is to occur on the
maximumrst24bitsaftertheaddress.Thesoftmenu
keyNUMBEROFBYTESallowsyoutodenehowmany
bytes are to be analyzed for the trigger condition. The
input may be binary or hexadecimal (PATTERN INPUT). If
binary input is selected, the individual bits can be
assigned to any condition via soft menu key SELECT BIT
Fig. 12.6: I
2
C data trigger menu
Fig. 12.7: I
2
C READ/WRITE trigger menu
Fig. 12.8: I
2
C BUS