NXP Semiconductors
LPCXpresso55S36UM
LPCXpresso55S36 Development Board User Manual
The USB-to-UART bridge (VCOM feature) can be disabled so that the target MCU
USART port can be used for other purposes. For example, to create an external UART
connection from USART connecter JP3 using a USB-to-serial cable.
The USB-to-UART bridge can be disabled by disabling voltage translator U22 (setting it
to high impedance). To disable U22, unpower the LPCXpresso55S36 board and short
jumper JP26. Shorting/opening JP26 after powering up the board has no impact on the
functions/features of the MCU-Link firmware. When VCOM feature is disabled, then the
target MCU UART port can be used for other purposes.
3.6 Connecting to a target through a USB-to-SPI or USB-to-I2C bridge
MCU-Link supports the USB serial input/output (USBSIO) port feature, which adds a
USB serial I/O port on the host computer, and connects it to the target MCU by using
MCU-Link as a USB-to-SPI bridge or USB-to-I2C bridge. Support for the USBSIO feature
can be enabled on the host computer using the libusbsio library, which is a free host
library from NXP for Windows/Linux/MacOS systems. For more details on the libusbsio
.
In the LPCXpresso55S36 board, MCU-Link is connected to the Flexcomm 8 (HS SPI)
port of the target MCU using slave select 1 connection, through a voltage translator
U24, which enables communication between MCU-Link and the target MCU, by shifting
voltage levels of signals between the two devices from 3.3 V to 3.3/1.9 V and vice versa.
MCU-Link is also connected to the Flexcomm 1 (I2C) port of the target MCU through an
I2C repeater / a voltage translator U27, which enables communication between MCU-
Link and the target MCU, by shifting voltage levels of signals between the two devices
from 3.3 V to 3.3/1.9 V and vice versa.
To use MCU-Link as a USB-to-SPI or USB-to-I2C bridge, the board must be connected
to the host computer through a USB cable from its J1 connector. A USB-to-SPI bridge
can be used to program the target MCU using the ISP mode and/or to emulate the host
system. A USB-to-I2C bridge can be used to program the target MCU using the ISP
mode and/or to emulate the host system / board peripherals. NXP MCUXpresso Secure
Provisioning Tool (SEC) provides an option to program the target via a USB-to-SPI or
USB-to-I2C bridge (see
The USBSIO feature can be disabled for SPI or I2C so that the target MCU SPI/I2C
port can be used for other purposes. Disabling this feature instructs the firmware not
to enumerate the USB endpoint for USBSIO (which is called “MCU-Link LPCSIO” for
backward compatibility reasons). Disabling the USBSIO feature also frees more USB
bandwidth for the SWO profiling and energy measurement features of MCU-Link.
The USBSIO feature can be disabled for SPI by disabling voltage translator U24 (setting
it to high impedance). To disable U24, unpower the LPCXpresso55S36 board and short
jumper JP57 (not populated on the board). Shorting/opening JP57 after powering up the
board has no impact on the functions/features of the MCU-Link firmware. When USBSIO
feature is disabled for SPI, then the target MCU SPI port can be used for other purposes.
The USBSIO feature can be disabled for I2C by opening jumper JP4.
3.7 Connecting to a target through a USB-to-GPIO bridge
The MCU-Link USBSIO feature also allows MCU-Link to be used as a USB-to-GPIO
bridge to connect the MCU-Link LPC55S69 target to the host computer. Support for the
USBSIO feature can be enabled on the host computer using the libusbsio library, which is
LPCXpresso55S36UM
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User manual
Rev. 2 — 5 September 2022
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