MCP2221 datasheet(21/80 Pages) MICROCHIP

21 / 80 page

 2015 Microchip Technology Inc.

DS20005292B-page 21

MCP2221

1.9

CLKR

When GP1 is configured for clock output operation, the

GP1 pin will act as a digital output, providing a clock

signal derived from the device’s internal clock. The

clock’s nominal frequency is 12 MHz ± 0.25%. Other

clock values and duty cycles are possible by setting

different values that are associated with this mode of

operation.

1.10

IOC

When GP1 is configured for Interrupt-on-Change (IOC)

operation, GP1 acts as a digital input that is sensitive to

positive and negative edges. Depending on the

settings associated with this mode of operation, the

GP1 can detect positive, negative or both edges.

1.11

RESET/POR

1.11.1

RESET PIN

The RST pin provides a method for triggering an

external Reset of the device. A Reset is generated by

holding the pin low. These devices have a noise filter in

the Reset path, which detects and ignores small

pulses.

1.11.2

POR

A POR pulse is generated on-chip whenever VDD rises

above a certain threshold. This allows the device to

start in the initialized state when VDD is adequate for

operation.

To take advantage of the POR circuitry, tie the RST pin

to VDD through a resistor (1 – 10 k

). This will

eliminate external RC components usually needed to

create a POR delay.

When the device starts normal operation (i.e., exits the

Reset

condition),

device

operating

parameters

(voltage, frequency, temperature, etc.) must be met to

ensure operation. If these conditions are not achieved,

the device must be held in Reset until the operating

conditions are met.

1.12

Internal Oscillator

The MCP2221 features an internal oscillator that

provides a 12 MHz clock, which is needed for the USB

modules (HID and CDC).

Full-speed USB is nominally 12 Mb/s. The clock

signal’s accuracy is over temp (2,500 ppm maximum).

The internal clock of the MCP2221 is fed into the CLKR

module to provide a clock signal outside of the device.

GP1 can be configured as a clock output pin providing

a 12 MHz clock to the rest of the system. Other clock

and duty-cycle values are possible by using different

settings for this module.

1.13

I2C™ Master Module

The I2C Master module is responsible for the I2C traffic

generation. The module is controlled through the USB

HID, through the Bus Matrix module.

The I2C module only implements the functionality of an

I2C/SMBus Master.

1.13.1

I2C/SMBUS MASTER

The I2C Master initiates all the I2C/SMBus transactions

(being read or write operations) on the bus.

The I2C/SMBus Master module has the following

capabilities:

• sending/receiving data at a multitude of bit rates,

up to 400 kbps

• 7-bit Addressing mode

• single data transfers of up to 65,535 bytes

• clock-stretching (it allows the slower I2C Slaves to

communicate)

All the user data to be sent/transmitted over the I2C bus

is conveyed to the USB host only through the USB HID

interface.

1.14

Bus Matrix Module

The Bus Matrix module manages the communication

between various functional modules, such as: USB

(HID and CDC), I2C, UART, GPIO/ADC/DAC, Config,

IOC, CLKR, Pin Mux.

1.15

Config Module

The Config module is in charge of the storage of the

device settings and also of their management

(loading/modifying/access protection). The module

uses non-volatile memory for storing the Power-Up

device settings.

At Power-Up, the module loads the settings from the

non-volatile storage area into an SRAM location

(volatile settings). These settings represent the

device’s configuration, along with other key parameters

(e.g., string descriptors, VID/PID, etc.). After the

settings are loaded in SRAM (volatile settings), they

can be changed through the USB HID interface.

The user can read/modify/change either settings

(nonvolatile or volatile) through the same interface

(USB HID).

The Config module contains the relevant Power-Up

settings that are used by the MCP2221. A few

examples of settings are: USB descriptors, GP

settings, ADC, DAC, CLKR.

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