Datasheet

MCP2221
DS20005292A-page 4  2014 Microchip Technology Inc.
1.1 Supported Operating Systems
The following operating systems are supported:
• Windows – XP (SP3)/Vista/7/8 and 8.1
•Linux
®
– any distribution with support for CDC
and HID classes
•Mac OS
®
– all versions, beginning with 10.7
1.1.1 ENUMERATION
The MCP2221 enumerates as a composite USB device
after Power-on Reset (POR). The device enumerates
as both a Human Interface Device (HID) for I
2
C, GPIO
control, and as CDC for the USB-UART converter.
1.1.1.1 USB HID
The MCP2221 enumerates as an HID, so the device
can be configured, while the I
2
C and GPIO can be con-
trolled. A DLL package, with example applications and
tools, is supplied by Microchip on the device web page,
on the Microchip web site www.microchip.com.
1.1.1.2 USB CDC
The CDC enumeration implements the USB-to-UART
data translation.
1.2 Bus-Matrix Module
The Bus-Matrix module is the heart of the MCP2221.
All other modules are tied together and controlled via
the Bus-Matrix module. This module manages the data
transfers between the USB and the UART, the I
2
C
Master module, as well as the command requests gen-
erated by the USB host controller, and commands for
controlling the function of the UART, GPIO, ADC, DAC
and Clock Output.
1.2.1 UART
The control module interfaces to the UART and USB
modules.
1.2.2 ACCESSING THE DEVICE
The MCP2221 can be accessed for reading and writing
via USB host commands. The device cannot be
accessed or controlled via the UART interface.
1.3 UART Interface
The MCP2221 UART interface consists of the Tx and
R
X data signals.
The UART is configurable for several baud rates. The
available baud rates are listed in Ta ble 1 -2 .
1.3.1 GET/SET LINE CODING
The GET_LINE_CODING and SET_LINE_CODING
commands are used to read and set the UART
parameters while in operation. For example, terminal
applications (e.g., Putty, RealTerm, Hyperterminal,
etc.) send the SET_LINE_COMMAND when connecting
to the port. The MCP2221 responds by setting the baud
rate only.
The other parameters (Data Bits, Parity, Stop Bits)
remain unchanged.
1.3.1.1 Rounding Errors
Primary baud rate settings (with associated rounding
errors) are shown in Table 1-2 .
If baud rates other than the ones shown in the table are
used, the error percentage can be calculated using
Equation 1-1 to find the actual baud rate.
EQUATION 1-1: SOLVING FOR ACTUAL
BAUD RATE
1.3.2 CUSTOM BAUD RATES
Custom baud rates are configured by sending the
SET_LINE_CODING USB command. See Section 2.0
“USB Enumeration Process”, for more information.
Note: MCP2221 supports only eight data bits,
No Parity and one Stop bit.
TABLE 1-2: UART PRIMARY BAUD
RATES
Desired Rate Actual rate % Error
300 300 0.00%
1200 1200 0.00%
2400 2400 0.00%
4800 4800 0.00%
9600 9600 0.00%
19200 19200 0.00%
38400 38339 0.16%
57600 57692 0.16%
115200 115385 0.16%
ActualRate
12MHz
int x
------------------=
Where:
x
12MHz
DesiredBaud
-----------------------------------=