Design Resources


The PE0003 Evaluation Kit Interface Card is a global interface system for use with evaluation kits for CML’s new generation ICs, including FirmASIC™ based products. This greatly simplifies the approach to the evaluation and design-in process. Link to:


The EV6550D Evaluation Kit is designed to assist in the evaluation and application development of the CMX655D. The EV6550D is designed to interface with MEMS (Micro-Electro Mechanical System) microphone evaluation boards. Knowledge Base


The EV6550D is now obsolete. Visit the Product Archive to download the support file.



The EV6550DHAT brings the benefits of MEMS (Micro-Electro Mechanical System) microphone technology and the CMX655D voice codec to the Raspberry Pi. This is achieved through the use of a standard Hardware on Top (HAT) design and supporting “C” based firmware and GUI (Graphical User Interface). The EV6550DHAT is now obsolete. Visit the Product Archive to download the support file.

Package: Q6

24-pin VQFN


Q: The CMX655D Ultra Low Powered Audio Codec with PA, supports 8, 16, 32 and 48ksps sampling rates, however my application requires a sampling rate of 44.1ksps, a common rate used in recording studios and for CD’s.  Should I consider the CMX655D?

A: The CMX655D Ultra Low power codec IC was developed to support portable and low powered applications such as handheld radios and intercoms systems, but it has been found useful in many other applications.

The CMX655D is a fully digital codec and as such all internal functions such as the filters and the sampling rates are derived from an internal 24.576 MHz clock.  For example, 24,576,000 / 512 = 48 kHz, one of the default sampling rates.  Therefore, it is possible to support 44.1 kHz by scaling this clock proportionately, for example while 48 kHz is set: 22,579,200 / 512 = 44.1 kHz

The internal 24.576 MHz clock may be sourced from the RCLK pin or from the integrated PLL.  A recent test was performed to demonstrate that 44.1 kHz operation using a clock sourced from the Serial Audio Interface (SAI) was possible.  To achieve this the CMX655D was operated as a clock slave with a 48 kHz sample clock (where the integrated PLL is set to be referenced to the sample period «LRCLK/FS»).  Then by sending audio samples via the SAI with a sample rate of 44.1 kHz, the audio could be reproduced accurately at the Class D, PA output.

It should be noted that this method may work with any sample rate from 32 kHz up to 48 kHz. All internal clocks will scale and will affect both the microphone and speaker audio paths.  However, it should be noted that the CMX655D would be operating outside the datasheet stated limits, so caution is required if attempting a new untested clock.

Note: The EV6550DHAT does not currently support sample rates outside those quoted in the CMX655D datasheet although possible with additional modification.

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