When I should set the GPIO to open drain mode or push-pull mode?

viprobin · ‎2012-01-12

Posted on January 12, 2012 at 13:30

There is a part of codes in the stm324xg_eval_audio_codec.c.

/* CODEC_I2C SCL and SDA pins configuration -------------------------------------*/

/* If the I2C peripheral is already enabled, don't reconfigure it */

if ((CODEC_I2C->CR1 & I2C_CR1_PE) != 0)

{

GPIO_InitStructure.GPIO_Pin = CODEC_I2C_SCL_PIN | CODEC_I2C_SDA_PIN;

GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF;

GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;

GPIO_InitStructure.GPIO_OType =

GPIO_OType_OD

;

GPIO_InitStructure.GPIO_PuPd = GPIO_PuPd_NOPULL;

GPIO_Init(CODEC_I2C_GPIO, &GPIO_InitStructure);

/* Connect pins to Periph */

GPIO_PinAFConfig(CODEC_I2C_GPIO,

CODEC_I2S_SCL_PINSRC

, CODEC_I2C_GPIO_AF);

GPIO_PinAFConfig(CODEC_I2C_GPIO,

CODEC_I2S_SDA_PINSRC

, CODEC_I2C_GPIO_AF);

}

/* CODEC_I2S pins configuration: WS, SCK and SD pins -----------------------------*/

GPIO_InitStructure.GPIO_Pin = CODEC_I2S_WS_PIN | CODEC_I2S_SCK_PIN | CODEC_I2S_SD_PIN;

GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF;

GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;

GPIO_InitStructure.GPIO_OType =

GPIO_OType_PP

;

GPIO_InitStructure.GPIO_PuPd = GPIO_PuPd_NOPULL;

GPIO_Init(CODEC_I2S_GPIO, &GPIO_InitStructure);

/* Connect pins to I2S peripheral */

GPIO_PinAFConfig(CODEC_I2S_GPIO, CODEC_I2S_WS_PINSRC, CODEC_I2S_GPIO_AF);

GPIO_PinAFConfig(CODEC_I2S_GPIO, CODEC_I2S_SCK_PINSRC, CODEC_I2S_GPIO_AF);

GPIO_PinAFConfig(CODEC_I2S_GPIO, CODEC_I2S_SD_PINSRC, CODEC_I2S_GPIO_AF);

I want to know why I2C and I2S use different modes. By the way, I think

CODEC_I2S_SCL_PINSRC

shoud be corrected to

CODEC_

I2C

_SCL_PINSRC.

#basic-electronics

Tesla DeLorean · ‎2012-01-12

Posted on January 12, 2012 at 13:45

I2C has always been a bidirectional interface using open collector/drain, slave devices recognize when they are addressed and need to signal back to the master. Push-pull would cause drivers to fight/contend with each other.

I2S is a single slave, point-to-point interface, as I recall.

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