Limitations and bugs

Chip or software limitations

USB speed limits

GPIO update rate GPIO_write(): 500Hz
GPIO read rate for GPIO_read(): 500Hz
ADC sample rate for ADC_read(): 500Hz.
DAC update rate for DAC_write(): 500Hz.

Internal reference reset

From MCP2221A’s datasheet (section 1.8):

When the Set SRAM settings command is used for GPIO control, the reference voltage for VRM is always reinitialized to the default value (VDD) if it is not explicitly set.

This is compensated by software. But, due to the calling interval, there will be always a 2ms gap in the DAC output if it is using internal reference (not Vdd) when you change any pin function.

I2C crashes

Eventually, due to a glitch or unexpected timeout, the MCP2221 cancels an I2C transfer. The slave may be in the middle of sending a byte, and expecting some clocks cycles to send the rest of the byte.

MCP2221 is unable to start a new I2C transfer while SDA line is still busy. And the slave won’t release SDA until next clock cycle. So the whole bus hangs.

See LowSDAError.

Misc

The ADC seems to be always connected. So leakage current for GP1, GP2 and GP3 is greater than for GP0. Think of it as a very weak pull-down resistor on these pins.
This library does not work with password protected devices. You cannot use it to set or clear MCP2221’s Flash password.
Changing VID/PID not supported.
Maximum length for single I2C read or write operations is 65535 bytes.

Software Bugs

None reported.

Bug tracking system: https://github.com/electronicayciencia/EasyMCP2221/issues