2015-2017 Microchip Technology Inc.
DS00001855E-page 15
USB5744
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
. The individual pin function assign-
ments for each mode are detailed in
. For additional device connection information, refer to
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 34
and
Section 9.6.3, "Reset and Con-
figuration Strap Timing," on page 35
. If configuration straps are not at the correct voltage level prior to being
latched, the device may capture incorrect strap values.
TABLE 3-9:
SPI/SMBUS MODE CONFIGURATION SETTINGS
Pin
SPI Mode
(
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 3-10:
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
