Testing the LVDS Connectors¶
The LVDS bus consists of two 50 pin flat ribbon cables conencting the DDS boards with the breakout boards. Unlike the digital output board there exists no board to test the conenctions visually with LEDs. The LVDS bus can be tested directly with a DDS board. For this the DDS board is connected to the breakout board. Then, a logic analyzer is programmed into the FPGA on the DDS board.
For this, one needs to install QUARTUS II, which is a software from Altera and a FPGA programming device USB blaster. The logic analyzer in QUARTUS II is called SignalTap. More information about SignalTap can be found in:
The SignalTap file is test_lvds_bus.stp. In order to download the logic analyzer into the FPGA, the USB blaster needs to be connected to the JTAG port on the DDS board (labelled J1). The correct JTAG file is dds_controller_stp_test_lvds_bus.sof
Now the test Test LVDS bus (Logic analyser) should be performed (see Testing the hardware of a complete PBox).
After applying the test, the state of the bus should be 0xaaaaaaaa. So all lines of the bus should be alternating high/low.
With the next test, the timing of the bus can be investigated. The SignalTap should cycle between the value 0xfffffffe and 0x00000000. The delay between two cycles hould be roughly 15 clock cycles.
If these tests are performed succesfully, the DDS board should work immediately after applying the 1GHz clock.
Most common hardware errors are:
- The terminators of the LVDS bus are not isntalled
- The connector between the mainboard and the breakout board is incorrectly soldered.
- The connectors of the flat ribbon cable are not properly attached.
- The clock of the DDS board is not connected
- The LVDS-TTL converters on the DDS board are incorrectly soldered.