Hardware description

UM1900

12/19

DocID027905 Rev 3

SB

Status

SB16

Open

SB17

Open

SB18

Open

SB19

Open

SB20

Open

SB21

Open

In addition, J2 must be placed in position 1-2 for on-board microphone acquisition or 2-3

when using an external microphone, while J3 must be left open. If using external

microphones, do not plug anything in M2_EXT header.

2 microphone acquisition

In this case, the I²S peripheral is used to generate twice the frequency needed by the

microphones. In this scenario, the clock is then halved by the timer and routed to the

microphones to give them the right clock. I²S therefore reads values from both edges of the

merged PDM lines. For this use case you need the following SB configuration:

Table 5: Solder bridge configuration for 2 microphone acquisition

SB

Status

SB7

Close

SB8

Open

SB9

Open /Close

SB10

Open

SB11

Close

SB12

Open

SB13

Close

SB14

Open

SB15

Close

SB16

Open

SB17

Open

SB18

Open

SB19

Open

SB20

Open

SB21

Open

In addition, J2 must be placed in position 1-2 for on-board microphone acquisition or 2-3

when using external microphones, while J3 must be left open. When acquiring on-board

microphones, close SB9 to acquire both of them.

4 external microphone acquisition

In this case, the I²S peripheral is used to generate a clock frequency that is twice the

frequency needed by the microphones, and SPI is configured in slave mode in order to use

such timing. As in the previous case, the clock is then halved by the timer and routed to the