User manual

51
Serial BUS Analysis
12.5.1 SPI / SSPI BUS Konguration
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. Use the top soft menu key SOURCE to se-
lect the respective channel for chip select (CS), clock (Clk)
and data. Select the respective soft menu key CS, Clk or
Data and then use the soft menu key DATA and the univer-
sal 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 pa-
ckets are shorter than the time out, these packets belong
to the same frame. You can select the dead time via uni-
versal knob or via numeric input (KEYPAD button). A small
window provides information about the current settings.
In addition to assigning the source, the soft menu key AC-
TIVE 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 sig-
Prior to the BUS conguration it is necessary to set the correct
logic level (threshold). Please refer to chapter 4.5. The default
setting is 500 mV. With 3-wire SPI the CS (chip select) has to be
connected to the external trigger input. The level can be set in
the BUS conguration menu via EXTERNAL LEVEL.
If the option R&S®HOO11 resp. the voucher R&S®HV111 is in-
stalled, it it only possible to select analog channels as source.
If the option R&S®HOO10 resp. the voucher R&S®HV110 is ins-
talled, both analog and digital channels are available as source.
Fig.12.10:MenuforthedenitionofaSPI BUS
and the universal knob. The soft menu key STATE allows
you to set the state H (=1), L (=0) or X (don’t care) for
eachbit.ThestateXdenesanystate.Iftheinputis
hexadecimal, only the entire byte can be set to X. If you
choose the hexadecimal input, use the soft menu key
VALUE and the universal knob to set the respective byte
value. The soft menu key SELECT BYTE allows you to
edit the different bytes (byte 1 to byte 2 to byte 3 etc.)
sequentially(dependingonthedenedNUMBEROF
BYTES). The active byte will be marked with a green
border in the display window of the trigger condition.
Press the MENU OFF button several times to close all
menus, and the oscilloscope will trigger on the set address
and data. For measurements without measuring object
please refer to chapter 12.2.2.
12.5 SPI / SSPI BUS
The Serial Peripheral Interface SPI is used to communicate
with slow peripheral devices, in particular for the transfer
of data streams. The SPI bus was developed by Motorola
(today known as Freescale); however, it has not been for-
mally standardized. Generally, this is a bus with clock and
data lines and a select line (3-wire). If only one master and
one slave are present, the select line may be deleted. This
type of line is also called SSPI (Simple SPI) (2-wire). A SPI
BUS has the following properties:
Master-slave communication
No instrument addressing
Noacknowledgetoconrmdatareception
Duplex capability
Most SPI buses have 4 common lines, 2 data lines and 2
control lines:
Clock to all slaves (SCLK)
Slave select or chip select lines (SS or CS)
Master-Out-Slave-In, Slave-Data-Input (MOSI or SDI)
Master-In-Slave-Out, Slave-Data-Output (MISO or SDO)
If the master generates a clock pulse and selects a
slave, data can be transmitted in either one direction or
simultaneously in both directions (only available with
R&S®HOO10/R&S®HV110).
.
For SPI/SSPI BUS trigger and decoding you need the R&S®HOO10
resp. R&S®HOO11 option or the upgrade voucher R&S®HV110
resp. R&S®HV111.
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.
Fig.12.9:SimplecongurationofaSPIBUS