Overview
A connected product needs a microcontroller with the right interfaces and a bus that stays reliable as the board grows, and NXP provides both the LPC family with USB, CAN and Ethernet and the I2C interface family that manages the buses. BeiLuo supplies them with genuine traceability and FAE support. This page shows how they fit together in a connectivity and interface design.
The Interfaces on the MCU
The LPC family covers the connectivity a modern product needs. The LPC11U68 provides a USB 2.0 device interface on an efficient Cortex-M0+ core, the LPC1768 provides USB host, device and OTG with Ethernet and CAN on a Cortex-M3 core, and the LPC54606 provides USB and Ethernet with a large SRAM on a Cortex-M4 core at 180 MHz. Choose the part from the interfaces the product must have, and confirm the peripheral and the pin count for the board.
USB and Ethernet
A USB interface on the MCU removes a separate controller, and the hashing and the buffering are handled on the chip. An Ethernet MAC on the larger parts suits a networking node, and the CAN interface suits an industrial bus. Confirm the reference clock and the magnetics for the interface you use.
Managing the Bus
As a board grows, the I2C bus collects more devices and the problems appear: an address conflict, too much capacitance and a section that must be isolated. The NXP PCA9548A 8-channel I2C switch fans the upstream pair out to eight sections, so a designer can isolate the noisy part, hot-plug a board, divide the capacitance and resolve the conflict, and it even translates the voltage between the two sides. Write the control register to select a channel, and use the reset input at power-up.
I/O Expansion
Where the product needs more ports, an NXP PCA9555 or PCA9554 adds sixteen or eight I/O over the same two wires, with an interrupt to the host. The address pins place several expanders and switches on one bus, so the design scales without a larger host.
The Host Interface to the Switch
The switch and the expanders share the same I2C host interface as the rest of the board, so the firmware manages them through the same driver, and the interrupt from an expander wakes the host on an input change. Plan the device map and the interrupt lines early, because a clear map makes the firmware and the debug simple.
Signal Integrity
Keep the bus traces short, use the pull-ups the speed and the voltage require and keep the total capacitance within the limit, dividing the bus with a switch where it grows large. A clean bus is what keeps a connected product reliable across the temperature range.
Verification
Validate the design on the bench by exercising the USB or the Ethernet interface at the worst case, by checking the I2C bus timing with a scope and by testing the switch and the expanders under load. Our FAE team can review the measurements and the layout, so the connected design performs in the product as it does on the bench.
Getting Help
Send your interface and I/O needs, the bus and the environment to our FAE team, and we will propose an LPC MCU and the I2C devices, help choose the part and the ports and review the bus and the signal integrity. BeiLuo holds mainstream NXP devices in regional stock and ships them with an import declaration, a certificate of origin and a RoHS compliance file, so a connectivity design can move from prototype to production without a supply gap.