Hardware
2018 Microchip Technology Inc.
Advance Information
DS50002762A-page 15
2.4
USING THE ISOLATED USB-UART INTERFACE
The board implements a galvanically isolated USB-UART interface based around the
MCP2221A chip. The MCP2221A implements the standard Communication Device
Class (CDC) – Abstract Control Model (ACM) protocol, and therefore, can use standard
USB drivers that are provided with modern Windows
®
, Mac
®
and Linux
®
operating
systems. Under most operating systems, the USB driver installation will be fully auto-
matic. Under certain older operating systems, or if the device is attached to an older than
Windows 10 machine without an active internet connection, manual installation of the
drivers may be necessary. In this case, the driver package can be downloaded from:
www.microchip.com/mcp2221a
Details on how to access the serial port from Mac and Linux operating systems can also
be found in the associated collateral for the MCP2221A. Under Windows, after
successful USB driver installation, the device will appear as a “COMx” port object,
which standard serial terminal programs can open/read/write to and from.
2.5
CIRCUIT DETAILS
Some of the circuit blocks in the schematics may not have immediately obvious
purpose or method of operation. This section highlights some of these circuit elements
and provides an explanation for their intent and function.
2.5.1
Jumpers/Headers/Connectors
J1
– This is an unpopulated 2-pin, 100 mil jumper header, which may optionally be used
to insert a current meter in series with the U1 V
DD
current path to measure the micro-
controller current consumption. In order to measure the U1 current, the trace on the
bottom of the PCB, that shorts the two pins of J1, should be cut and a 2-pin jumper
should be soldered into J1.
J2
– This is an unpopulated 6-pin staggered header interface, which can optionally be
used to connect an external programmer/debugger tool to the target microcontroller
U1. Ordinarily, it is not necessary to use J2, since the integrated programmer/debugger
(PKOB) circuit connects to the same U1 program/debug interface pins.
J3
– This is a female header that implements the mikroBUS Interface A, which can be
used to attach hardware daughter boards to expand the functionality of the
development board.
J8
– This is a female header that implements the mikroBUS Interface B, which can be
used to attach hardware daughter boards to expand the functionality of the
development board.
J10
– This jumper sets the -3 dB low-pass filter breakpoint frequency of the RC
network, composed of R54 + C26/C41. When the jumper is open, the low-pass filter
frequency is around 15.9 kHz, but with the jumper capped, it is around 1.4 kHz. When
a sufficiently high-frequency PWM waveform is generated on RC5, the low-pass filter
can smooth it into a near DC value, which is buffered by op amp U8, providing a
software controlled DAC capability.
J11
– This is a female I/O pin access header used for accessing the U1 microcontroller
I/O pins.
J12
– This is a female I/O pin access header used for accessing the U1 microcontroller
I/O pins.