USB5744

DS00001855D-page 16

 2015-2016 Microchip Technology Inc.

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 CONFIGURATION

The SPI/SMBus pins can be configured into one of two functional modes:

• SPI Mode

• SMBus Slave Mode

If 10 k

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

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

SPI Mode. The strap settings for these supported modes are detailed in Table 3-10. The individual pin function assign-

ments for each mode are detailed in Table 3-11. For additional device connection information, refer to Section 4.0,

"Device Connections".

Note 4:

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:

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 35 and Section 9.6.3, "Reset and Con-

figuration Strap Timing," on page 36. If configuration straps are not at the correct voltage level prior to being

latched, the device may capture incorrect strap values.

TABLE 3-10:

SPI/SMBUS MODE CONFIGURATION SETTINGS

Pin

SPI Mode

(Note 4)

SMBus Slave Mode

39

(SPI_DO)

No pull-up/down

10 k

 pull-up

38

(SPI_CLK)

No pull-up/down

10 k

 pull-up

TABLE 3-11:

SPI/SMBUS MODE PIN ASSIGNMENTS

Pin

SPI Mode

SMBus Slave Mode

41

SPI_CE_N

CFG_NON_REM

40

SPI_DI

CFG_BC_EN

39

SPI_DO

SMDAT

38

SPI_CLK

SMCLK