Hi,
We have the ZOOM OMAPL138 evaluation board that has a spare SPI0 port that will be connected to a DAC7654 eval board.
The software guy has created a simple routine to write to the SPI0 port.
We belieive we have the timing for the SPI interface to match the DAC7654 datasheet.
However when the voltage swing on the SIMO (SDI on DAC) board is only ~1.8Vpp. The CS and CLK line are full 3.3V swing.
With no DAC board connected (OMAP board only) @ startup the SIMO line are 3.3V swing and then after the s/w code is initialized it goes to 1.8V. Our DAC7654 requires Vih =2.3V min.
I looked through the user manual for the OMAP but couldn't find a register that changes the voltage swing for the SPI lines .
I see in the schematics for the ZOOM card that there are power groups for the DVDD3318(ABC) so that you can select from 3.3 or 1.8. I believe the default is 3.3 so this should not be an issue.
I did also notice there is a voltage translation cct for the other SPI1 port. Is this required for the SPI interfaces?
Below is how we intend to connect the OMAP SPI interface to the DAC board.
Any help is greatly appreciated... i have already lost too many hairs on a simple SPI interface.
OMAP EVAL Pin/Signal | DAC Signal |
GPIO0[1] | LDAC |
GPIO0[0] | LOAD |
J29(9) / SPI0_SCS0 | CS |
J13(10) / SPI0_CLK | SCLK |
J13(12) / SPI0_SOMI | SDO |
J13(14) / SPI0_SIMO | SDI |
GPIO | Reset |