User manual

Operating Basics

AM700 Audio Measurement Set User Manual

2-41

DSP Port. You can connect a compatible digital microphone or other compatible

digital signal source directly to the DSP for processing through the DSP Port

connector (pinout shown in Figure 2-33). When the AM700 generator and input are

set to DSP, the external device on the DSP port supplies the Bit Clock, Frame Clock,

and Receive Data. When sending data, the AM700 supplies Transmit Data that is

synchronized with Bit and Frame Clocks of the external device. Rate 0, Rate 1, Rate

2, Flag 0, and Flag 1 are reserved for future use. The DSP port timing diagram is

shown in Figure 2-34.

The external device connected to the DSP port determines the sampling rate. The

sampling rate to the AM700 must be no greater than 48 kHz. Also, the generator

audio sample rate must match the incoming sample rate with the Interface Clock

Frequency control set to Audio Sample Rate. Applications will yield correct

measurement values only if the sample rate of the DSP input signal is 32 MHz, 44.1

MHz, or 48 MHz, and the AM700 is set to match. The incoming signal must also

have a 16-bit audio word in order to be correctly acquired by the hardware.

A valid signal must be applied to the DSP port when selecting the DSP input. If not,

the AM700 halts in the waiting-for-clock mode. Bit and Frame Clocks must always

be clean, with no extra transitions, while the AM700 is in DSP mode. If extra

transitions occur, the clock register can overflow and halt operation of the digital

audio board. If this occurs, the AM700 must be powered off and back on to clear the

mode when switching the sample rate of any external device attached to the DSP

port. The maximum input voltage for the DSP port is –0.5 V to +5.5 V. For good

noise immunity, the rise and fall time of the transitions should be less than 100 ns.

NOTE. The DSP generator must be selected to permit the DSP to acquire input from

the DSP port.