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Digital control board debugging notes (view source)
Revision as of 15:38, 30 September 2010
, 15:38, 30 September 2010no edit summary
This page contains a list of all currently known problems with the digital control board.
This page contains a list of all currently known problems with the digital control board.
== Resistor on DAC temperature measurement diode too high ==
=== Description ===
When the readout is programmed using the DAC manual's coefficients and offset, the temperature value ends up tens of degrees off.
=== Cause/Solution ===
The board was designed with R1=270kΩ to sink the current from the DAC's internal temperature-measuring diode to ground. The manual specifies the expected diode drop at 25degC will be 0.65V at a current of 100uA. Given the sensitivity of this device (with a coefficient of 2.2mV/degC) it is seems best to match their measurement conditions and adjust the resistor so that 0.65V drop from the biasing 5V results in 100uA through the resistor. So, ''R1 should be set to 43.5kΩ''.
Three parallel resistors have been soldered into place on the prototype board providing a nominal R1 of 43.6kΩ. The readout values are now reasonable.
=== Solution ===
=== Solution ===
The diode was rotated on all the prototyping boards. This indications has '''not yet been entered into the layout'''.
The diode was rotated on all the prototyping boards. This indication has '''not yet been entered into the layout'''.
=== Other Details and Current Status ===
=== Other Details and Current Status ===
== Mismatched JTAG programming header ===
== Mismatched JTAG programming header ==
=== Description ===
=== Description ===
The connector of the "Xilinx Platform USB II" kit seems to be a reduced size compared to the standard 0.1" spaced pin header with which the board is equipped.
The connector of the "Xilinx Platform USB II" kit seems to be a reduced size compared to the standard 0.1" spaced pin header with which the board is equipped.
=== Solution ===
=== Solution ===
For the testing stage, the flying lead connector is sufficient to bypass this problem. The layout must be corrected to the matching header (type?). Change entered already?
For the testing stage, the flying lead connector is sufficient to bypass this problem. The layout must be corrected to the matching header (type?). Change entered already?
== Ethernet jack pinout mismatch ==
The wrong Ethernet jack was attached to the PCB, leading to a pinout mismatch. The part ordered was the Pulse J001'''1'''D21. The correct part is J001'''2'''D21. The correct part was ordered and soldered onto the prototype boards, but this change must be made in the Altium parts list.
= Suggested/Preferred Changes =
* <code>R12</code>, the pull-up resistor for the reset pins (header 2) is unnecessary, as the FPGA pin can be programmed to pull up.