USB5734 datasheet(17/61 Pages) MICROCHIP

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DS00001854D-page 17

USB5734

3.4

Configuration Straps and Programmable Functions

Configuration straps are multi-function pins that are used during Power-On Reset (POR) or external chip reset

(RESET_N) to determine the default configuration of a particular feature. The state of the signal is latched following de-

assertion of the reset. Configuration straps are identified by an underlined symbol name. This section details the various

device configuration straps and associated programmable pin functions.

3.4.1

SPI/SMBUS/I2C/UART CONFIGURATION (I2C_SLV_CFG[1:0])

The SPI/SMBus/I2C//UART pins can be configured into one of four functional modes:

• SPI Mode

• SMBus Slave Enable Mode

•I2C Bridging Mode

•UART Mode

If 10 k

 pull-up resistors are detected on SPI_DO and SPI_CLK, the SPI/SMBus/I2C/UART pins are configured into

SMBus Slave Enable Mode. If a 10 k

 pull-down resistor is detected on SPI_DO, the SPI/SMBus/I2C/UART pins are

configured into UART Mode. If no pull-ups or pull-downs are detected on SPI_DO and SPI_CLK, the SPI/SMBus/I2C/

UART pins are first configured into SPI Mode. If no valid SPI ROM is detected, the SPI/SMBus/I2C/UART pins are con-

figured into I2C Bridging Mode. The strap settings for these supported modes are detailed in Table 3-11. The individual

pin function assignments for each mode are detailed in Table 3-12. For additional device connection information, refer

to Section 4.0, "Device Connections".

Note 6:

In order to use the SPI interface, an SPI ROM containing a valid signature of 2DFU (device firmware

upgrade) beginning at address 0xFFFA must be present. Refer to Section 7.1, "SPI Master Interface" for

additional information.

Note 7:

In order to use the SMBus slave interface, the SPI_DO and SPI_CLK pins must be configured for SMBus

Slave Enable Mode and CFG_STRAP must be configured to Configuration 1, 2, 3, or 6, which programs the

PROG_FUNC4 and PROG_FUNC5 pins as SMDAT and SMCLK, respectively. When in Configuration 4 or

5, the SMBus slave interface is not usable. Refer to Section 3.4.5, "Device Mode / PROG_FUNC[7:1] Con-

figuration (CFG_STRAP)" for additional information.

Note 8:

In order to use the I2C Bridging interface, the SPI_DO and SPI_CLK pins must be configured for I2C Bridg-

ing Mode and CFG_STRAP must be configured to Configuration 1, 2, 3, or 6, which programs the PROG_-

FUNC4 and PROG_FUNC5 pins as SMDAT and SMCLK, respectively. When in Configuration 4 or 5, the

I2C Bridging interface is not usable. Additional hub register configuration is also required. Refer to Section

3.4.5, "Device Mode / PROG_FUNC[7:1] Configuration (CFG_STRAP)" and Section 7.3, "I2C Bridge Inter-

face" for additional information.

Note:

The system designer must guarantee that configuration straps meet the timing requirements specified in

Section 9.6.2, "Power-On and Configuration Strap Timing," on page 46 and Section 9.6.3, "Reset and Con-

figuration Strap Timing," on page 47. If configuration straps are not at the correct voltage level prior to being

latched, the device may capture incorrect strap values.

Note:

The following interfaces cannot be used simultaneously:

• UART and SMBus Slave

• UART and SPI

• SMBus Slave and I2C Bridging interface

TABLE 3-11:

SPI/SMBUS/I2C/UART MODE CONFIGURATION SETTINGS

SPI Mode

(Note 6)

SMBus Slave Enable

Mode (Note 7)

I2C Bridging

Mode (Note 8)

UART

Mode

(SPI_DO)

No pull-up/down

10 k

 pull-up

No pull-up/down

10 k

 pull-down

(SPI_CLK)

No pull-up/down

10 k

 pull-up

No pull-up/down

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