Hameg HMO Series, Manual

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51
Subject to change without notice
S e r i a l b u s a n a l y s i s
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 highlighted by the
menu key in blue.
The
SLAVE ADDRESS
is the address used on the BUS to dis -
tinguish which slave the master communicates with. Use the
universal knob to select the address for the observing bus
participant to be triggered.
Fig. 13.9: I 2 C data trigger menu
The soft menu
DATA
enables you to enter specific data in addi-
tion to the address. With this menu, you can trigger on clearly
defined data bytes (color cyan) within the transmission, allowing
you to filter 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
defines the distance between the bytes relevant for the trig-
ger condition and the address. In most cases, the byte offset
is zero if the trigger is to occur on the maximum first 24 bits
after the address. The soft menu key
NUMBER OF BYTES
allows
you to define 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
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 defines 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
defined NUMBER OF BYTES). The active byte will be marked with a
green border in the display window of the trigger condition (see fig.
13.9). Press the MENU OFF button three times to close all menus,
and the oscilloscope will trigger on the set address and data.
13.4 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 formally 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).
The HMO series supports the following bit rates (for measure -
ments without measuring object via BUS SIGNAL SOURCE):
– 100 kBit/s,
– 250 kBit/s and
– 1 MBit/s.
Fig. 13.11: SPI BUS signal source
Use the soft menu PROBE COMP & BUS SIGNAL SOURCE to
select the respective clock rate in the SETUP menu (page 2|2).
A SPI BUS has the following properties:
– Master-slave communication
– No instrument addressing
– No acknowledge to confirm 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.
Fig. 13.12: Simple configuration of a SPI BUS Fig. 13.10: Example I
2
C BUS with BUS table