This is a library for interfacing with the HID features of the MCP2221 USB to UART and I2C/SMBus serial converter from Microchip and the newer MCP2221A. The converter includes 4 GPIO pins, 3x 10-bit ADCs, 1x 5-bit DAC and more.
Microchip does provide a library for interfacing with the chip, however it is supplied as proprietary DLLs. This project aims to be an open-source and multi-platform alternative.
This library also makes use of HIDAPI.
| Feature | Status |
|---|---|
| ADC | Supported |
| DAC | Supported |
| GPIO | Supported |
| Interrupt input | Supported |
| Clock reference output | Supported |
| USB Descriptors (Manufacturer, product, serial, VID, PID) |
Supported |
| I2C/SMB | Limited support, WIP |
| Flash password protection | Not yet implemented |
| C++ and C# wrappers | Not yet implemented |
Documentation
Bits of info about the MCP2221
- Doesn’t use a crystal, only requires 1 small capacitor when powered with 3.3V or 2 capacitors when powered with 5V.
- Available in a hacker friendly DIP package.
- Has a remote wake function which when used in conjunction with the interrupt input can be used to wakeup the USB host (usually a PC), just like waking up from a keyboard or mouse press.
- The raw value of the I2C pins can also be read, allowing them to be used as an additional 2 general purpose input pins.
- Unfortunately there are no options for enabling any internal pull-up/down resistors.
- The MCP2221 seems to be a PIC16F1455. [Source]
- Current consumption @ 3.3V with USB disconnected can be anywhere between 20uA and 70uA, not sure what causes such a difference. Remote wakeup needs to be disabled (default) otherwise current consumption will be about 5mA.
- Kinda slow compared to other USB/UART converters. Even with the baud rate set to 1,000,000 its overall throughput is only about 250,000 bps. More about this below.
Unconnected pins
The usual way to deal with unconnected pins are to enable their internal pull-up/down resistors, but this chip doesn’t support them. Instead it’s probably best to set unconnected pins as output high or low.
The I2C pins are a little different since they can’t be set to outputs, though there’s still few options:
| I2C Pin | Description |
|---|---|
| Unconnected | Bad, floating inputs will cause excessive power consumption |
| Connect to VDD | Bad, if the I2C bus is accidentally used then a short circuit will occur |
| Connect to ground | OK, but may cause the I2C bus to hang if used, not much of an issue though |
| External pull-up resistors | Best option, but requires additional components |
UART Throughput
The main UART function seems to be really slow, maxing out at about 250,000 bps throughput when set to 1,000,000 baud due to a gap of about 30us after each byte transmitted. This isn’t much of a problem at lower bauds, but as the baud rate increases it creates a huge overhead (75% @ 1Mbaud!). Attempting to receive data without a sufficient gap will also corrupt the data. Here are some screen shots comparing the MCP2221 and CH340 UART converter ICs transmitting data at 1,000,000 baud. The MCP2221 has a gap of about 30us between each byte, while the CH340 has a gap of just 1us.
MCP2221 @ 1Mbaud
CH340 @ 1Mbaud
Other issues
If the MCP2221 receives too much UART data too soon after powering up it will have trouble enumerating with the USB host.
MCP2221A
The MCP2221A replaces the MCP2221 and is fully compatible with this library. The new chip appears to have fixed the USB enumeration issue described above and the gap between each transmitted UART byte now varies from 4us to 18us, but usually around 6us.
A breakout module for the MCP2221, design available on the GitHub repo
5 comments
1 ping
Skip to comment form
Wow, that look like good work.
What kind of timescale for C# wrapper to be beta released?
Have you tried C# code under Visual Studio, how they performed?
Thanks
Author
Hey, the C# wrapper will probably be made when I start working on a project that needs it. There is currently such a project on my to do list, but I’ve still got a number of other things happening before I can start on it. So I can’t really say when, sorry.
VS is the only IDE I’ve used for C# stuff. It performs alright, but can be a bit clunky at times.
I confirm MCP2221 is a PIC16F1455, naturally CP is ON.
This is the dump of config*
8007 CONFIG1 F44 FOSC INTOSC Oscillator Selection Bits INTOSC oscillator: I/O function on CLKIN pin
WDTE OFF Watchdog Timer Enable WDT disabled
PWRTE ON Power-up Timer Enable PWRT enabled
MCLRE ON MCLR Pin Function Select MCLR/VPP pin function is MCLR
CP ON Flash Program Memory Code Protection Program memory code protection is enabled
BOREN ON Brown-out Reset Enable Brown-out Reset enabled
CLKOUTEN OFF Clock Out Enable CLKOUT function is disabled. I/O or oscillator function on the CLKOUT pin
IESO OFF Internal/External Switchover Mode Internal/External Switchover Mode is disabled
FCMEN OFF Fail-Safe Clock Monitor Enable Fail-Safe Clock Monitor is disabled
8008 CONFIG2 1FCD WRT HALF Flash Memory Self-Write Protection 000h to 0FFFh write protected, 1000h to 1FFFh may be modified by PMCON control
CPUDIV NOCLKDIV CPU System Clock Selection Bit NO CPU system divide
USBLSCLK 48MHz USB Low SPeed Clock Selection bit System clock expects 48 MHz, FS/LS USB CLKENs divide-by is set to 8.
PLLMULT 3x PLL Multipler Selection Bit 3x Output Frequency Selected
PLLEN ENABLED PLL Enable Bit 3x or 4x PLL Enabled
STVREN ON Stack Overflow/Underflow Reset Enable Stack Overflow or Underflow will cause a Reset
BORV LO Brown-out Reset Voltage Selection Brown-out Reset Voltage (Vbor), low trip point selected.
LPBOR OFF Low-Power Brown Out Reset Low-Power BOR is disabled
LVP OFF Low-Voltage Programming Enable High-voltage on MCLR/VPP must be used for programming
Maybe a day we can got also the firmware
Hi
I have a question
What are the function
GPIO_init() ADC_Init() , API is not cleared
If I call GPIO_Init() does it mean all pins are now GPIO
what If I want PIN1 to be GPIO, and PIN2 to Be ADC
Thanks
Author
Hey Josh, there are no API functions named GPIO_init() or ADC_Init() in this library.
[…] MCP2221 HID Library – [Link] […]