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RX Tech Notes

RX devices not working with Optibit interface


Product: RX
Version: Serial numbers RX5 < 4000, RX6, RX7, RX8 < 2000
Date Added: 2012-06-26


Older RX devices (see serial numbers above) will not work with the FO5 Optibit interface.


Use the FI5 interface with affected RX devices.


The switch to Optibit required a modification to the RX motherboards not found on older units on older units. Contact TDT for assistance.

RMS2 component produces erroneous output


Product: RX, RZ
Version: < 71
Date Added: 2010-10-15


The output of the RMS2 component doesn't behave correctly for large inputs and tends to grow unbounded.


Upgrade to the latest version of TDT Drivers and OpenEx. This was resolved in TDT drivers v71. Upgrade to v71 or above and reprogram the microcode on your RX or RZ.

Buffering a long signal at a high sample rate causes a memory allocation error


Product: RX, ActiveX
Version: All
Date Added: 2006-12-04


The memory allocation for the buffer on an RX device is 14450300 samples. When the buffer required exceeds this limit a memory allocation error is reported.


Either use two buffers each holding half of the data then use ScaleAdd to sum them together, or compress the data into 16-bit integers and expand back into 32-bit floats on the hardware.

If the signal can be expressed in 16-bit format, use the ActiveX command WriteTagVEX and ExpandFrom16 as shown in the figure below. Scale the input data so the maximum values scale to ± 32767. Write the 16-bit data to the Data port of the source component. Expand from 16 to 32 bits using the ExpFrom16 component with the inverse of the scale factor used in the first step. Note: not recommended for 32-bit signals such as wav files or signals acquired on a TDT device.

This Matlab example assumes an input to the SerSource component bounded by unity:

s = 1:2000;
s = sin(s); % input bounded by unity
s = s*32760; % scale the data to best fit the range +/- 32767

2000 16-bit input data points fit into the SerSource buffer of size 1000.

RX devices intermittently fail to boot


Product: RX
Version: RX5, RX7, RX8 serial numbers < 5000 and RX6 serial numbers < 3000
Date Added: 2006-09-20


RX devices, when paired with the FO5 Optibit Gigabit Interface, will intermittently fail to boot properly. The failure is on the circuits in right side of the device. When this problem occurs, the BITS LEDs will fail to light and the affected RXn device will show up as an RX5 in zBusMon. This problem is most common when an RX device with 5 DSPs is used with the FO5 Optical Gigabit Interface.


The following tips can be used to mitigate the problem:

  1. Turn devices on one at a time starting with the first rack in the hardware loop.

  2. If a device fails to boot, cycle the power on that device only.

  3. Leave the devices on whenever possible; a rack of 4 RX devices draws less power than a light bulb.


When it's convenient, contact TDT to request an RMA for an upgrade.

External anti-aliasing devices -- are they necessary?


Product: RZ, RX
Version: All
Date Added: 2004-09-23


Anti-aliasing is built in to all processors with sigma-delta DACs or ADCs, including the RX6, RA16SD, RP2.1, RL2, RM1, RM2, and RA16BA. You do not need an external anti-aliasing filter with these devices.

Devices which use PCM DACs or ADCs, such as the RA16PA, RX5, and RV8D do not have a built-in anti-aliasing filter, so it might be necessary to use an external anti-aliasing filter with these devices.

Random and intermittent failure of programmable devices


Product: RP2, RX, RZ
Version: All
Date Added: 2002-11-27


The real-time processors can intermittently fail to boot if there is an external device connected to the Digital I/O port on the device.


Remove any cable connected to the digital I/O on your processor before booting it up. Replace the cable once the device is fully booted.

Increased signal noise on DAC outputs when viewed with an oscilloscope


Product: RP2, RX, RZ
Version: All
Date Added: 2002-12-17


An oscilloscope samples at a much higher rate than the processors run at. Users may see increased signal noise beyond the Nyquist frequency. If the sampling rate is set properly, the noise is above the hearing range of your subject and has insufficient power to have any physiological effect.


Sample at a higher rate or filter the signal after it is sent from the device.


If signal is acquired on another device, make sure that other device is running at a sampling rate at least as fast as your TDT processor to avoid aliasing artifacts.