side logic level. The SS#, SCK, and MOSI line will be left in their default enabled
state, and will be shifted up to the Adapter/Analyzer's logic level.
•
MONITOR:
When selected, will leave all SPI lines in their default enabled state,
and will therefore be shifted up to the Adapter/Analyzer side logic level. This
option is used in situations where only a Beagle I C/SPI/MDIO analyzer is
plugged into the board, and no SPI adapter is being used.
•
DISABLE:
When selected, will disable all Target side SPI outputs, and set them to
a high-impedance state. If no connection is set, the board will default to this state.
However, if any of the previous con
fi
guration is set, it will take precedence on this
one.
It is important to note that for most all cases only one of these connections should be set
at a time. Using more than one may cause incorrect SPI operation. The only situation in
which more than one jumper may be used is if the SPI lines are being used for GPIO.
4.4 MDIO Level Shifting
The MDIO signal lines are shared with SPI. It is therefore not possible to bidirectionally
shift MDIO signals, as the SPI level shifting does not have the infrastructure for this.
However, MDIO
monitoring
of lower logic levels is still possible. Simply place the SPI
control jumper on
MONITOR
, and set the Beagle I C/SPI/MDIO analyzer to monitor
MDIO.
4.5 GPIO Level Shifting
GPIO signals may fall on either I C lines or SPI lines, and each of these situations must
be handled separately. When the GPIO lines coincide with the SPI lines, special care
must be taken to ensure that the SPI level shifting circuit is con
fi
gured to the correct
direction. The SPI lines are logically broken up into two separate groups: the master-
driven lines (SS#, SCK, MOSI) and the slave-driven line (MISO). The direction of each of
these groups can be controlled independently, but all signals within a group will be in the
same direction.
Placing a jumper on the MASTER header will enable the master-driven lines to down-
shift, and the slave-driven line to up-shift. Placing a jumper on the SLAVE header will
enable the slave-driven line to down-shift, and the master-driven lines to up-shift. Placing
a jumper on the MONITOR header will enable all lines to up-shift. If there is ever a time
when a line is con
fi
gured to be both up-shifting and down-shifting, the down-shift will
take precedence. Thus, if you want to use all the SPI lines as digital outputs from the
host adapter, simply place jumpers on
both
the MASTER and SLAVE headers.
Level Shifter Board User Manual v1.01
2
2
2
14
注3 つまり MDIO用としては、低電圧のMDIOバスを3,3Vレベルに一方向だけレベルシフトするmonitor用途
しか想定していません。 MDIOマスタデバイスまたはスレーブデバイスのレベルシフトを行いたい場合、
立野電脳(株)へご相談ください。