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Subject to change without notice
S e r i a l b u s a n a l y s i s
13.4.1 SPI / SSPI BUS Configuration
Prior to the BUS configuration it is necessary to set
the correct logic level for the digital channels (see
chapter 11.2) or the analog channels (see chapter
4.5). The default setting for both is 500 mV. For the
two channel instruments, the CS (chip select) must
be connected to the external trigger input; the level
can be set at the setup menu of the bus under CON-
FIGURATION
>
EXTERNAL LEVEL.
Make sure that a complete message of a serial pro-
tocol is always displayed on the screen to ensure
decoding can function properly. The Zoom function
allows you to view details for any specific message.
Certain settings are necessary to guarantee that a SPI bus is
decoded correctly. First, you have to determine if a SPI system
with or without chip select is available (2-wire or 3-wire SPI).
This can be done in the BUS setup menu when selecting the
BUS type. For a 2-wire SPI system, select the option SSPI; for
a 3-wire SPI system, select the option SPI.
Then press the
CONFIGURATION
button to open the setup
menu for SPI.
Fig. 13.13: Menu for the definition of a SPI bus
Use the top soft menu key
SOURCE
to select the respective
channel for chip select (CS), clock (Clk) and data. Select the
respective soft menu key CS, Clk or Data (key will be high-
lighted in blue) and then use the soft menu key DATA and the
universal knob to the select the respective source channel. For
the 2-wire SPI, select the possible
TIME OUT
instead of a chip
select
source. During the time out, data and clock line are at
Low. When the time out has been reached, a new frame begins.
If the time intervals between the data packets are shorter than
the time out, these packets belong to the same frame. You can
select the dead time via universal knob or via numeric input
(KEYPAD button). A small window provides information about
the current settings (see fig. 13.13).
If the option HOO10 is installed, it is possible to se-
lect analog and digital channels as source. For the
installed option HOO11, only the analog channels
are available as source. For two channel instru-
ments and a 3-wire SPI, the chip select signal has
to be connected to the external trigger input.
In addition to assigning the
source, the soft menu key ACTIVE
allows you to select the following settings:
CS:
Chip select high or low active (low active is the default
setting)
CLK:
Data will be stored with rising or falling slope (rising
slope is the default setting)
DATA:
Data high or low active (high active is the default
setting)
You can use the soft menu key
BIT ORDER
to determine if the
data of each message starts with the MSB (most significant
bit) or the LSB (least significant bit). The soft menu key WORD
SIZE allows you to select via universal knob how many bits are
included per message. You may select any value between 1
and 32 bits.
13.4.2 SPI / SSPI BUS Triggering
After the
BUS configuration, it will be possible to trigger on
various events. Press the TYPE button in the TRIGGER section of
the control panel and choose the soft menu key
SERIAL BUSES
.
Then press the SOURCE button in the TRIGGER section and
choose SPI Bus. This will only be available if it was configured
earlier. Press the FILTER button in the TRIGGER section of the
control panel to list all available
SPI
trigger conditions.
Fig. 13.14: SPI trigger menu
The option FRAME START sets the trigger event on the start of
the frame. The frame starts when the chip select (CS) signal
switches to the selected active mode. By contrast, FRAME ENDE
sets the trigger event on the end of the frame. The frame ends
when the chip select (CS) signal switches from the selected
active to the inactive mode. The soft menu key BIT and the
universal knob allow you to select the trigger time to the set
bit within the set bit sequence. You can also enter a numeric
value to determine the desired bit number (KEYPAD button).
Use the soft menu
SER. PATTERN
to define a specific bit se-
quence within the frame which start the trigger event. The soft
menu key
BIT OFFSET
allows you to select the first bit of the
predefined bit sequence within the frame. The bits in front of
it have no impact on the trigger event (for instance, if the bit
offset = 2, bit 0 and bit 1 after CS will be ignored and the pat-
tern begins with bit 2). You can select a value between 0 and
4095 via
universal knob or enter it numerically (KEYPAD but-
ton). The soft menu key NUMBER OF BITS allows you to select
how many bits will be analyzed for the trigger condition. You
can select a value between 1 and 32 bit via universal knob. The
serial bit sequence (PATTERN INPUT) can be entered as binary
or hexadecimal value.
