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Fig 2: Yellow is BUSA output, green is BUSB, Red is the ACTIVE trigger signal
7. The HI-1590 can also read back data from the DAC register but only after a value has been
written into the register. Press the 'D' key, type in '80', the previous setting of 'FF' should be
read out as shown below. Observe the amplitude on the scope; this should be reduced by
half, or approximately 12V p-p.
8. The SPI software has a ramp function, this ramps the amplitude on both outputs up to
maximum and back down to zero in a 'sawtooth' function. Press the 'Y' button and observe
the amplitude rising and falling. Whilst in this mode switch the VSEL switch to 'Low', this
selects the low amplitude, you should see the oscilloscope trace go down to one fifth
maximum amplitude or about 5V.
9. As well as SPI control of amplitude through a DAC, the HI-1590 has the option of using an
analog voltage of 0 to 3.3VDC to control the amplitude. To use this feature move the jumper
10
AN-1590
Holt Integrated Circuits
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