AM2754-Q1: How to Connect AM275 EVM with A2B Mic

Hello Kevin,

We have a few options for connecting external devices to the mcasp interface on the AM275x EVM. 

1. Use a breakout board/connector board to utilize the on-board expansion connector (Audio Expansion Connectors - AEC)
2. Use the on-EVM J28 header and configure the device to route MCASP to the header (MCASP4)

1. Using a breakout board: Using a Zebax ZX146-QTE-QSE-040 is the easiest option because it gives you a breakout board that can be used in-line to sniff signals, but can also be used to connect other peripherals to the audio expansion connector. This connector is directional and can only be plugged in 1 way, so there is no need to worry about plugging it in wrong. The pins on the card are labeled and match the pinouts described in the AM275x EVM's Userguide: AM275x Audio EVM User Guide in the AEC Mapping section (2.11 at the time of writing). There are 2 AEC connectors on this board, so depending on which MCASP channels (or how many) you require, you may need 2x of these breakout boards), but generally should be ok with just 1.

2. Using the on-EVM J28 header

This uses a header onboard to route MCASP4 signals out, but does require some additional code. 

In the user guide, you'll see the pinout for J28 is as follows (on the A revision of the board)
J28[1] - MCASP4_ACLKX
J28[2] - MCASP_AXR5_MLB0_DAT
J28[3] - MCASP4_ACLKR
J28[4] - MCASP_AXR4_MLB0_CLK
J28[5] - MCASP4_AFXS
J28[6] - MCASP_AXR3_MLB0_SIG
J28[7] - MCASP4_AFSR
J28[8] - MCASP_AXR0

In order to these signals to be routed to the J28 header, you must first select the desired voltage domain of the J28 header with the J29 header. The middle pin (J29[2]) should be shorted to either pin 1 for 1.8V or pin 3 for 3.3V.

In addition, your software will need to command the I2C-controlled switch to route the signals to the J28 header instead of the default AEC connector. The simpliest way is to modify your project's board.c file (a file which normally contains the configuration information for the ADC and DAC used on the EVM), but these modifications can go anywhere.

a. Include the following file for controlling the IO expander

#include "board/ioexp/ioexp_tca6416.h"

b. Add the following function to tell the switch to route the signals

int32_t Board_MuxSelMcASP4(void)
{
    int status;
    uint32_t pinNum = 3;

    TCA6416_Config  TCA6416_Config;
    TCA6416_Params  tca6416Params;
    TCA6416_Params_init(&tca6416Params);
    tca6416Params.i2cInstance = CONFIG_I2C0;
    tca6416Params.i2cAddress = 0x20;
    TCA6416_open(&TCA6416_Config, &tca6416Params);


    status = TCA6416_setOutput(
                    &TCA6416_Config,
                    pinNum,
                    TCA6416_OUT_STATE_LOW);

    /* Configure as output  */
    status += TCA6416_config(
                    &TCA6416_Config,
                    pinNum,
                    TCA6416_MODE_OUTPUT);

    status = TCA6416_setOutput(
                    &TCA6416_Config,
                    pinNum,
                    TCA6416_OUT_STATE_HIGH);

    return status;
}

c. This function should be called after the I2C interface is initialized, but before you setup mcasp.

Make sure you update your sysconfig file to point to the correct mcasp ports.