USBtin (also called canUSB), is a project that allows sending and receiving can messages from a USB host machine. The hardware and software design was done by Thomas Fischl, and more information can be learned from his page . When plugged into a computer the board creates a (CDC) serial port. This makes interfacing very easy.
The normal 9600 baud works well to connect the usb serial port to a terminal program. On windows I use putty as a serial port terminal.
CanUSB does not echo characters, and the newlines are set up in a linux way. So I force echo characters, and newline for every return line.
The list of commands is as follows.
| Sx[CR] | Set baudrate |
| x: Bitrate id (0-8) | |
| S0 = 10 kBaud | |
| S1 = 20 kBaud | |
| S2 = 50 kBaud | |
| S3 = 100 kBaud | |
| S4 = 125 kBaud | |
| S5 = 250 kBaud | |
| S6 = 500 kBaud | |
| S7 = 800 kBaud | |
| S8 = 1 MBaud | |
| sxxyyzz[CR] | Set can bitrate registers of MCP2515. You can set non-standard baudrates which are not supported by the "Sx" command. |
| xx: CNF1 as hexadecimal value (00-FF) | |
| yy: CNF2 as hexadecimal value (00-FF) | |
| zz: CNF3 as hexadecimal value | |
| Gxx[CR] | Read MCP2515 register. xx: Address of MCP2515 register to read as hexadecimal value (00-FF). |
| Wxxyy[CR] | Write MCP2515 register. xx: Address of MCP2515 register to write. Hexadecimal value (00-FF). |
| yy: Data to write to the register. Hexadecimal value (00-FF). | |
| V[CR] | Get hardware version. |
| v[CR] | Get firmware version. |
| N[CR] | Get serial number. Returns always 0xffff. |
| O[CR] | Open CAN channel. |
| l[CR] | Open device in loop back mode. |
| L[CR] | Open CAN channel in listen-only mode. |
| C[CR] | Close CAN channel |
| tiiildd..[CR] | Transmit standard (11 bit) frame. |
| iii: Identifier in hexadecimal format (000-7FF) | |
| l: Data length (0-8) | |
| dd: Data byte value in hexadecimal format (00-FF) | |
| Tiiiiiiiildd..[CR] | Transmit extended (29 bit) frame. |
| iiiiiiii: Identifier in hexadecimal format (0000000-1FFFFFFF) | |
| l: Data length (0-8) | |
| dd: Data byte value in hexadecimal format (00-FF) | |
| riiil[CR] | Transmit standard RTR (11 bit) frame. |
| iii: Identifier in hexadecimal format (000-7FF) | |
| l: Data length (0-8) | |
| Riiiiiiiil[CR] | Transmit extended RTR (29 bit) frame. |
| iiiiiiii: Identifier in hexadecimal format (0000000-1FFFFFFF) | |
| l: Data length (0-8) | |
| F[CR] | Read status/error flag of can controller |
| Return: Fxx[CR] with xx as hexadecimal byte with following error flags: | |
| Bit 0 - not used | |
| Bit 1 - not used | |
| Bit 2 - Error warning (Bit EWARN of MCP2515) | |
| Bit 3 - Data overrun (Bit RX1OVR or RX0OVR of MCP2515) | |
| Bit 4 - not used | |
| Bit 5 - Error-Passive (Bit TXEP or RXEP of MCP2515) | |
| Bit 6 - not used | |
| Bit 7 - Bus error (Bit TXBO of MCP2515) | |
| Zx[CR] | Set timestamping on/off. |
| x: 0=off, 1=on | |
| mxxxxxxxx[CR] | Set accpetance filter mask. SJA1000 format (AM0..AM3). Only first 11bit are relevant. |
| xxxxxxxx: Acceptance filter mask | |
| Mxxxxxxxx[CR] | Set accpetance filter code. SJA1000 format (AC0..AC3). Only first 11bit are relevant. |
| xxxxxxxx: Acceptance filter code |
The code for the board is on our github, here.
There are two program on the pic currently. A loader program and a canUSB program. The loader away starts first. If the jumper is off the loader jumps to the canUSB program. If the jumper is on the loader waits for a new hex file.
If you want to program the board via USB, a jumper should be placed on bootloader jumper. The board will identify has an HID (human interface device). A program like mphidflash, can be used to load on new hex file on the board.
This project is very similar to several other commercially used products.