Digital Serial Reference Clock

Created on 2013-08-22 23:47:00

Using the APx Digital Serial Output as Reference Clock

How can I generate a reference clock from APx?

A new feature in APx500 v3.4 (to be released soon) allows you to use an existing Digital Serial I/O option to generate a reference clock tied to the APx internal clock. You can output a reference clock signal from the module in any configuration where the signal path is not Digital Serial Input. The rate of the reference clock is arbitrary, and configured independently of the internal converter sample rates or other digital I/O rates.

In APx500 v3.4, a new monitor panel allows you to activate this feature and set the frequency quickly and easily, as illustrated below:

DSIO Reference Clock Monitor Panel

The signal produced is a 50% duty cycle square wave of 3.3 Vpp with a range of 4 kHz to 216 kHz. Accuracy is ±0.0003% (3 PPM), and the output impedance is 50 ohms.

Accessing the DSIO Clock

As show below, the clock signal appears on pin 5 of the Digital Serial I/O Receiver HD15 jack. Pins 2, 4, 6, 7, 10, 12 and 14 are grounded, and pins 1, 3, 8, 9, 13, 15 are Off. Bit Clock (64x) appears on pin 11.

HD15 DSIO Pinout


For this task, it is recommended that you use an Audio Precision CAB-DSIO cable kit. The green “FRAME” cable connects to pin 5 and to a grounded pin.