4.2 I C Level Shifting
The I C level shifting circuit automatically handles the bi-directionality of I C
communication. Simply select the correct logic level (as described previously) and
correctly connect the SCL and SDA lines of the master and slave.
4.3 SPI Level Shifting
Unlike I C, the SPI level shifting logic must be explicitly controlled for direction. The four
headers on the right side of the board determine the direction of tra
ffi
c. Selections are
made by placing a jumper on one of the headers. Their uses are described below:
Figure 11
: The Level Shifter Board must be con
fi
gured
from the correct mode of operation when using this board to
interface with an SPI or an MDIO bus.
•
MASTER:
When selected, will con
fi
gure the Adapter/Analyzer side of the board to
behave as the SPI master. Thus, the SS#, SCK, and MOSI lines will be shifted
down to the Target side logic level. The MISO line will be left in its default enabled
state, and will be shifted up to the Adapter/Analyzer's logic level.
•
SLAVE:
When selected, will con
fi
gure the Adapter/Analyzer side of the board to
behave as the SPI slave. Thus, the MISO line will be shifted down to the Target
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