Full API reference

Device Initialization

class Device(VID=1240, PID=221, devnum=0)

MCP2221(A) device

Parameters

VID (int, optional) – Vendor Id (default to 0x04D8)
PID (int, optional) – Product Id (default to 0x00DD)
devnum (int, optional) – Device index if multiple device found with the same PID and VID.

Raises

RuntimeError – if no device found with given VID and PID.

Example

>>> import EasyMCP2221
>>> mcp = EasyMCP2221.Device()
>>> print(mcp)
{
    "Chip settings": {
        "Power management options": "enabled",
        "USB PID": "0x00DD",
        "USB VID": "0x04D8",
        "USB requested number of mA": 100
    },
    "Factory Serial": "01234567",
    "GP settings": {},
    "USB Manufacturer": "Microchip Technology Inc.",
    "USB Product": "MCP2221 USB-I2C/UART Combo",
    "USB Serial": "0000000000"
}

Pin configuration

set_pin_function(gp0=None, gp1=None, gp2=None, gp3=None, out0=False, out1=False, out2=False, out3=False)

Configure pin function and, optionally, output value.

You can set multiple pins at once.

Accepted functions depends on the pin.

GP0 functions:

GPIO_IN (in) : Digital input
GPIO_OUT (out): Digital output
SSPND (out): Signals when the host has entered Suspend mode
LED_URX (out): UART Rx LED activity output (factory default)

GP1 functions:

GPIO_IN (in) : Digital input
GPIO_OUT (out): Digital output
ADC (in) : ADC Channel 1
CLK_OUT (out): Clock Reference Output
IOC (in) : External Interrupt Edge Detector
LED_UTX (out): UART Tx LED activity output (factory default)

GP2 functions:

GPIO_IN (in) : Digital input
GPIO_OUT (out): Digital output
ADC (in) : ADC Channel 2
DAC (out): DAC Output 1
USBCFG (out): USB device-configured status (factory default)

GP3 functions:

GPIO_IN (in) : Digital input
GPIO_OUT (out): Digital output
ADC (in) : ADC Channel 3
DAC (out): DAC Output 2
LED_I2C (out): USB/I2C traffic indicator (factory default)

Parameters

gp0 (str, optional) – Function for pin GP0. If None, don’t alter function.
gp1 (str, optional) – Function for pin GP1. If None, don’t alter function.
gp2 (str, optional) – Function for pin GP2. If None, don’t alter function.
gp3 (str, optional) – Function for pin GP3. If None, don’t alter function.
out0 (bool, optional) – Logic output for GP0 if configured as GPIO_OUT (default: False).
out1 (bool, optional) – Logic output for GP1 if configured as GPIO_OUT (default: False).
out2 (bool, optional) – Logic output for GP2 if configured as GPIO_OUT (default: False).
out3 (bool, optional) – Logic output for GP3 if configured as GPIO_OUT (default: False).

Raises

ValueError – If invalid function for that pin is specified.
ValueError – If given out value for non GPIO_OUT pin.

Examples

Set all pins at once:

>>> mcp.set_pin_function(
...     gp0 = "GPIO_IN",
...     gp1 = "GPIO_OUT",
...     gp2 = "ADC",
...     gp3 = "LED_I2C")
>>>

Change pin function at runtime:

>>> mcp.set_pin_function(gp1 = "GPIO_IN")
>>>

It is not permitted to set the output of a non GPIO_OUT pin.

>>> mcp.set_pin_function(
...     gp1 = "GPIO_OUT", out1 = True,
...     gp2 = "ADC", out2 = True)
Traceback (most recent call last):
...
ValueError: Pin output value can only be set if pin function is GPIO_OUT.
>>>

Only some functions are allowed for each pin.

>>> mcp.set_pin_function(gp0 = "ADC")
Traceback (most recent call last):
...
ValueError: Invalid function for GP0. Could be: GPIO_IN, GPIO_OUT, SSPND, LED_URX
>>>

Hint

Pin assignments are active until reset or power cycle. Use save_config() to make this configuration the default at next start.

save_config()

Write current status (pin assignments, GPIO output values, DAC reference and value, ADC reference, etc.) to flash memory.

You can save a new configuration as many times as you wish. That will be the default state at power up.

Raises

RuntimeError – if command failed.
AssertionError – if an accidental flash protection attempt was prevented.

Example

Set all GPIO pins as digital inputs (high impedance state) at start-up to prevent short circuits while breadboarding.

>>> mcp.set_pin_function(
...     gp0 = "GPIO_IN",
...     gp1 = "GPIO_IN",
...     gp2 = "GPIO_IN",
...     gp3 = "GPIO_IN")
>>> mcp.DAC_config(ref = "OFF")
>>> mcp.ADC_config(ref = "VDD")
>>> mcp.save_config()

GPIO

GPIO_read()

Read all GPIO pins logic state.

Returned values can be True, False or None if the pin is not set for GPIO operation. For an output pin, the returned status is the actual value.

Returns: 4 logic values for the pins status gp0, gp1, gp2 and gp3.
Return type: tuple of bool

Example

>>> mcp.GPIO_read()
(None, 0, 1, None)

GPIO_write(gp0=None, gp1=None, gp2=None, gp3=None)

Set pin output values.

If a pin is omitted, it will preserve the value.

To change the output state of a pin, it must be assigned to GPIO_IN or GPIO_OUT (see set_pin_function()).

Parameters

gp0 (bool, optional) – Set GP0 logic value.
gp1 (bool, optional) – Set GP1 logic value.
gp2 (bool, optional) – Set GP2 logic value.
gp3 (bool, optional) – Set GP3 logic value.

Raises

RuntimeError – If given pin is not assigned to GPIO function.

Examples

Configure GP1 as output (defaults to False) and then set the value to logical True.

>>> mcp.set_pin_function(gp1 = "GPIO_OUT")
>>> mcp.GPIO_write(gp1 = True)

If will fail if the pin is not assigned to GPIO:

>>> mcp.set_pin_function(gp2 = 'DAC')
>>> mcp.GPIO_write(gp2 = False)
Traceback (most recent call last):
    ...
RuntimeError: Pin GP2 is not assigned to GPIO function.

ADC

ADC_read()

Read all Analog to Digital Converter (ADC) channels.

Analog value is always available regardless of pin function (see set_pin_function()). If pin is configured as output (GPIO_OUT or LED_I2C), the read value is always the output state.

ADC is 10 bits, so the minimum value is 0 and the maximum value is 1023.

Returns: Value of 3 channels (gp1, gp2, gp3).
Return type: tuple of int

Examples

All three pins configured as ADC inputs.

>>> mcp.ADC_config(ref = "VDD")
>>> mcp.set_pin_function(
...    gp1 = "ADC",
...    gp2 = "ADC",
...    gp3 = "ADC")
>>> mcp.ADC_read()
(185, 136, 198)

Reading the ADC value of a digital output gives the actual voltage in the pin. For a logic output 1 is equal to Vdd unless something is pulling that pin low (i.e. a LED).

>>> mcp.set_pin_function(
...    gp1 = "GPIO_OUT", out1 = True,
...    gp2 = "GPIO_OUT", out2 = False)
>>> mcp.ADC_read()
(1023, 0, 198)

ADC_config(ref='VDD')

Configure ADC reference voltage.

ref values:

“OFF”
“1.024V”
“2.048V”
“4.096V”
“VDD”

Parameters: ref (str, optional) – ADC reference value. Default to supply voltage (Vdd).
Raises: ValueError – if ref value is not valid.

Examples

>>> mcp.ADC_config()

>>> mcp.ADC_config("1.024V")

>>> mcp.ADC_config(ref = "5V")
Traceback (most recent call last):
...
ValueError: Accepted values for ref are 'OFF', '1.024V', '2.048V', '4.096V' and 'VDD'.

Hint

ADC configuration is saved when you call save_config() and reloaded at power-up. You only need to call this function if you want to change it.

DAC

DAC_write(out)

Set the DAC output value.

Valid out values are 0 to 31.

To use a GP pin as DAC, you must assign the function “DAC” (see set_pin_function()). MCP2221 only have 1 DAC. So if you assign to “DAC” GP2 and GP3 you will see the same output value in both.

Parameters: out (int) – Value to output (max. 32) referenced to DAC ref voltage.

Examples

>>> mcp.set_pin_function(gp2 = "DAC")
>>> mcp.DAC_config(ref = "VDD")
>>> mcp.DAC_write(31)
>>>

>>> mcp.DAC_write(32)
Traceback (most recent call last):
...
ValueError: Accepted values for out are from 0 to 31.

DAC_config(ref='VDD', out=None)

Configure Digital to Analog Converter (DAC) reference.

ref values:

“OFF”
“1.024V”
“2.048V”
“4.096V”
“VDD”

MCP2221’s DAC is 5 bits. So valid values for out are from 0 to 31.

out parameter is optional and defaults last value. Use DAC_write() to set the DAC output value.

Parameters

ref (str, optional) – Reference voltage for DAC. Default to supply voltage (Vdd).
out (int, optional) – value to output. Default is last value.

Raises

ValueError – if ref or out values are not valid.

Examples

>>> mcp.set_pin_function(gp2 = "DAC")
>>> mcp.DAC_config(ref = "4.096V")

>>> mcp.DAC_config(ref = 0)
Traceback (most recent call last):
...
ValueError: Accepted values for ref are 'OFF', '1.024V', '2.048V', '4.096V' and 'VDD'.

Hint

DAC configuration is saved when you call save_config() and reloaded at power-up. You only need to call this function if you want to change it.

I2C

I2C_Slave(addr, force=False, speed=100000)

Create a new I2C_Slave object.

See EasyMCP2221.I2C_Slave.I2C_Slave for detailed information.

Parameters: addr (int) – Slave’s I2C bus address
Returns: I2C_Slave object.

Example

>>> pcf    = mcp.I2C_Slave(0x48)
>>> eeprom = mcp.I2C_Slave(0x50)
>>> eeprom
EasyMCP2221's I2C slave device at bus address 0x50.

I2C_write(addr, data, kind='regular', timeout_ms=20)

Write data to an address on I2C bus.

Valid values for kind are:

regular
It will send start, data, stop (this is the default)

restart
It will send repeated start, data, stop

nonstop
It will send start, data to write, (no stop). Please note that you must use ‘restart’ mode to read or write after a nonstop write.

Parameters

addr (int) – I2C slave device base address.
data (bytes) – bytes to write. Maximum length is 65535 bytes, minimum is 1.
kind (str, optional) – kind of transfer (see description).
timeout_ms (int, optional) – maximum time to write data chunk in milliseconds (default 20 ms). Note this time applies for each 60 bytes chunk. The whole write operation may take much longer.

Raises

ValueError – if any parameter is not valid.
NotAckError – if the I2C slave didn’t acknowledge.
TimeoutError – if the writing timeout is exceeded.
LowSDAError – See I2C_cancel().
LowSCLError – See I2C_cancel().
RuntimeError – if some other error occurs.

Examples

>>> mcp.I2C_write(0x50, b'This is data')
>>>

Writing data to a non-existent device:

>>> mcp.I2C_write(0x60, b'This is data'))
Traceback (most recent call last):
...
EasyMCP2221.exceptions.NotAckError: Device did not ACK.

Note

MCP2221 writes data in 60-byte chunks.

The default timeout of 20 ms is twice the time required to send 60 bytes at the minimum supported rate (47 kHz).

MCP2221’s internal I2C engine has additional timeout controls.

I2C_read(addr, size=1, kind='regular', timeout_ms=20)

Read data from I2C bus.

Valid values for kind are:

regular
It will send start, data, stop (this is the default)

restart
It will send repeated start, data, stop

Parameters

addr (int) – I2C slave device base address.
size (int, optional) – how many bytes to read. Maximum is 65535 bytes. Minimum is 1 byte.
kind (str, optional) – kind of transfer (see description).
timeout_ms (int, optional) – time to wait for the data in milliseconds (default 20 ms). Note this time applies for each 60 bytes chunk. The whole read operation may take much longer.

Returns

data read

Return type

bytes

Raises

ValueError – if any parameter is not valid.
NotAckError – if the I2C slave didn’t acknowledge.
TimeoutError – if the writing timeout is exceeded.
LowSDAError – See I2C_cancel().
LowSCLError – See I2C_cancel().
RuntimeError – if some other error occurs.

Examples

>>> mcp.I2C_read(0x50, 12)
b'This is data'

Write then Read without releasing the bus:

>>> mcp.I2C_write(0x50, position, 'nonstop')
>>> mcp.I2C_read(0x50, length, 'restart')
b'En un lugar de la Mancha...'

Hint

You can use I2C_read() with size 1 to check if there is any device listening with that address.

There is a device in 0x50 (EEPROM):

>>> mcp.I2C_read(0x50)
b'1'

No device in 0x60:

>>> mcp.I2C_read(0x60)
Traceback (most recent call last):
...
EasyMCP2221.exceptions.NotAckError: Device did not ACK.

Note

MCP2221 reads data in 60-byte chunks.

The default timeout of 20 ms is twice the time required to receive 60 bytes at the minimum supported rate (47 kHz). If a timeout or other error occurs in the middle of character reading, the I2C may get locked. See I2C_cancel().

I2C_speed(speed=100000)

Set I2C bus speed.

Acceptable values for speed are between 50kHz and 400kHz.

Parameters

speed (int) – Bus clock frequency in Hz. Default bus speed is 100kHz.

Raises

ValueError – if speed parameter is out of range.
RuntimeError – if command failed (I2C engine is busy).”

Example

>>> mcp.I2C_speed(100000)
>>>

I2C_cancel()

Try to cancel an active I2C read or write command.

Returns

True if device is now ready to go. False if the engine is not idle.

Return type

bool

Raises

LowSDAError – if I2C engine detects the SCL line does not go up (read exception description).
LowSCLError – if I2C engine detects the SDA line does not go up (read exception description).

Examples

Last transfer was cancel, and engine is ready for the next operation:

>>> mcp.I2C_cancel()
True

Last transfer failed, and cancel failed too because I2C bus seems busy:

>>> mcp.I2C_cancel()
Traceback (most recent call last):
...
EasyMCP2221.exceptions.LowSCLError: SCL is low. I2C bus is busy or missing pull-up resistor.

Note

Do not call this function without issuing a I2C_read() or I2C_write() first. It could render I2C engine inoperative until the next reset.

>>> mcp.reset()
>>> mcp.I2C_is_idle()
True
>>> mcp.I2C_cancel()
False

Now the bus is busy until the next reset.

>>> mcp.I2C_speed(100000)
Traceback (most recent call last):
...
RuntimeError: I2C speed is not valid or bus is busy.
>>> mcp.I2C_cancel()
False
>>> mcp.I2C_is_idle()
False
>>> mcp.I2C_cancel()
False

After a reset, it will work again.

>>> mcp.reset()
>>> mcp.I2C_is_idle()
True

I2C_is_idle()

Check if the I2C engine is idle.

Returns: True if idle, False if engine is in the middle of a transfer (timeout detected).
Return type: bool

Example

>>> mcp.I2C_is_idle()
True
>>>

Clock output

clock_config(duty, freq)

Configure clock output frequency and Duty Cycle.

duty values:

0
25
50
75

freq values:

“375kHz”
“750kHz”
“1.5MHz”
“3MHz”
“6MHz”
“12MHz”
“24MHz”

To output clock signal, you also need to assign GP1 function to CLK_OUT (see set_pin_function()).

Parameters

duty (int) – Output duty cycle in percent.
freq (str) – Output frequency.

Raises

ValueError – if any of the parameters is not valid.

Examples

>>> mcp.set_pin_function(gp1 = "CLK_OUT")
>>> mcp.clock_config(50, "375kHz")
>>>

>>> mcp.clock_config(100, "375kHz")
Traceback (most recent call last):
...
ValueError: Accepted values for duty are 0, 25, 50, 75.

>>> mcp.clock_config(25, "175kHz")
Traceback (most recent call last):
...
ValueError: Freq is one of 375kHz, 750kHz, 1.5MHz, 3MHz, 6MHz, 12MHz or 24MHz

USB wake-up

enable_power_management(enable=False)

Enable or disable USB Power Management options for this device.

Set or clear Remote Wake-up Capability bit in flash configuration.

If enabled, Power Management Tab is available for this device in the Device Manager (Windows). So you can mark “Allow this device to wake the computer” option.

A device reset() (or power supply cycle) is needed in order for changes to take effect.

Parameters

enable (bool) – Enable or disable Power Management.

Raises

RuntimeError – If write to flash command failed.
AssertionError – In rare cases, when some bug might have inadvertently activated Flash protection or permanent chip lock.

Example

>>> mcp.enable_power_management(True)
>>> print(mcp)
...
    "Chip settings": {
        "Power management options": "enabled",
...
>>> mcp.reset()
>>>

wake_up_config(edge='none')

Configure interruption edge.

Valid values for edge:

none: disable interrupt detection
raising: fire interruption in raising edge (i.e. when GP1 goes from Low to High).
falling: fire interruption in falling edge (i.e. when GP1 goes from High to Low).
both: fire interruption in both (i.e. when GP1 state changes).

In order to trigger, GP1 must be assigned to IOC function (see set_pin_function()).

To wake-up the computer, Power Management options must be enabled (see enable_power_management()). And “Allow this device to wake the computer” option must be set in Device Manager.

Parameters: edge (str) – which edge triggers the interruption (see description).
Raises: ValueError – if edge detection given.

Example

>>> mcp.wake_up_config("both")
>>>

Device reset

reset()

Reset MCP2221.

Reboot the device and load stored configuration from flash.

This operation do not reset any I2C slave devices.

Low level and debug

SRAM_config(clk_output=None, dac_ref=None, dac_value=None, adc_ref=None, int_conf=None, gp0=None, gp1=None, gp2=None, gp3=None)

Low level SRAM configuration.

Configure Runtime GPIO pins and parameters. All arguments are optional. Apply given settings, preserve the rest.

Parameters

clk_output (int, optional) – settings
dac_ref (int, optional) – settings
dac_value (int, optional) – settings
adc_ref (int, optional) – settings
int_conf (int, optional) – settings
gp0 (int, optional) – settings
gp1 (int, optional) – settings
gp2 (int, optional) – settings
gp3 (int, optional) – settings

Raises

RuntimeError – if command failed.

Examples

>>> from EasyMCP2221.Constants import *
>>> mcp.SRAM_config(gp1 = GPIO_FUNC_GPIO | GPIO_DIR_IN)

>>> mcp.SRAM_config(dac_ref = ADC_REF_VRM | ADC_VRM_2048)

Note

Calling this function to change GPIO when DAC is active and DAC reference is not Vdd will create a 2ms gap in DAC output.

send_cmd(buf)

Write a raw USB command to device and get the response.

Write 64 bytes to the HID interface, starting by buf bytes. Then read 64 bytes from HID and return them as a list. In case of failure (USB read/write or command error) it will retry. To prevent this, set cmd_retries to zero.

Parameters: buf (list of bytes) – Full data to write, including command (64 bytes max).
Returns: Full response data (64 bytes).
Return type: list of bytes

Example

>>> from EasyMCP2221.Constants import *
>>> r = mcp.send_cmd([CMD_GET_GPIO_VALUES])
[81, 0, 238, 239, 238, 239, 238, 239, 238, 239, 0, 0, 0, ... 0, 0]

Exceptions

To capture EasyMCP2221.exceptions you must qualify them as EasyMCP2221.exceptions:

try:
    mcp.I2C_read(0x51, 1)
except EasyMCP2221.exceptions.NotAckError:
    print("No device")
    exit()
except EasyMCP2221.exceptions.LowSCLError:
    print("SCL low")

or import them explicitly:

from EasyMCP2221.exceptions import *

...

try:
    mcp.I2C_read(0x51, 1)
except NotAckError:
    print("No device")
    exit()
except LowSCLError:
    print("SCL low")

exception NotAckError: I2C slave device did not acknowledge last command or data. Possible causes are incorrect I2C address, device missing or busy.

exception TimeoutError

I2C transaction timed out.

Possible causes:

I2C bus noise
incorrect command, protocol or speed
slave device busy (e.g. EEPROM write cycle)

exception LowSCLError

SCL remains low.

SCL should go up when I2C bus is idle.

Possible causes:

Missing pull-up resistor or too high.
Signal integrity issues due to noise.
A slave device is using clock stretching to indicate it is busy.
Another device is using the bus.

exception LowSDAError

SDA remains low.

SDA should go up when I2C bus is idle.

Possible causes:

Missing pull-up resistor or too high.
Signal integrity issues due to noise.
An I2C read transfer timed out while slave was sending data, and now the I2C bus is locked-up. Read the Hint.

Hint

About the I2C bus locking-up.

Sometimes, due to a glitch or premature timeout, the master terminates the transfer. But the slave was in the middle of sending a byte. So it is expecting a few more clocks cycles to send the rest of the byte.

Since the master gave up, it will not clock the bus anymore, and so the slave won’t release SDA line. The master, seeing SDA line busy, refuses to initiate any new I2C transfer. If the slave does not implement any timeout (SMB slaves do have it, but I2C ones don’t), the I2C bus is locked-up forever.

MCP2221’s I2C engine cannot solve this problem. You can either manually clock the bus using any GPIO line, or cycle the power supply.