The CAN Daughterboard

The CAN Daughterboard is an open-hardware CAN/SPI/I2C/Serial board designed by the Trustworthy Systems group at Data61/CSIRO, that can be mounted below the power supply module of the TK1-SOM. It provides two CAN buses implemented with MCP2515 (on the TK1-SOM’s SPI bus) and voltage conversion for the two serial ports.

Top of board Bottom of board Side view of mounted stack

Mounting

The board attaches to the bottom of a TK1-SOM via the expansion connector. No further work should be needed to enumerate the device given a kernel supporting GPIO chipselects.

Note the unpopulated standoff holes on the rightmost image above — it is possible to fit a standoff of the same type already installed in the TK1-SOM to stabilize the ‘tower’ making it easier to work with.

The part numbers of the standoffs between the CAN daughterboard and TK1 is the same as is already used between the CPU & GPU board. Order codes:

  • STANDOFF - HEX M2.5 x 16MM ALUMINUM M-F (M2111-2545-AL) between pcb standoff
  • SCREW - M2.5 x 5 MM SS PAN HEAD PHILIPS (92000A103) bottom pcb screw

Using Linux with this daughterboard for CAN

(hello world & testing) See Using CAN on L4T through an MCP251X

Pinout detail

The font on the silkscreen indicating pins is difficult to see once the tower is assembled (wasn’t enough space on the top) - See this picture (view taken from bottom):

Silk Screen

Warning - UART Level Converter:

  • If using the level converter on the board, and if you are getting junk from your 3V3 serial cable, read this:
  • Unfortunately there is an issue with these level converter chips, in some impedance situations the rise time is much worse than indicated on the datasheet. Basically, with some serial cables the converter will garble signals at a high baud rate (> 57600).
  • This can be circumvented by changing your u-boot and extlinux to use a slower baud rate. 9600 is very safe, anything up to about 57600 should be fine — start slow and work up.

If you need the faster baud rates (or don’t want to change the default settings), use a 1V8 USB-TTL cable and plug it straight into the TK1 as usual. This will be fixed in a future revision.

TK1 SOC Connections

Useful for writing drivers - this is a list of which pins on the board correspond to which SOC pins:

Note: All I2C signals operate at 3V3 on their 0.1” headers, except I2C_CAM which is selectable from 1V8<->3V3 in software.

PIN BALL PERIPHERAL ID
I2C_CAM_SCL AF8 I2C3_CLK
I2C_CAM_SDA AG8 I2C3_DAT
I2C_TK1_SCL Y2 I2C2_CLK
I2C_TK1_SDA AA2 I2C2_DAT
I2C_LOCAL_SCL P6 I2C1_CLK
I2C_LOCAL_SDA M6 I2C1_DAT

All SPI signals out of the TK1 are at 1V8, but are translated to 3V3 by the board (the 0.1” header operates at 3V3)

PIN BALL PERIPHERAL ID
SPI_CLK AG15 SPI1A_SCK
SPI_MISO AL18 SPI1A_DIN
SPI_CSN AL16 SPI1A_CS0
SPI_MOSI AK17 SPI1A_DOUT

All UART signals out of the TK1 are at 1V8, but are translated to 3V3 by the board. Note that UART signals will only be present on the board outputs if the uart is actually jumpered to the converter!

PIN BALL PERIPHERAL ID
J8_RTSn V5 UD3_RTS
J8_CTSn V9 UD3_CTS
J8_TXD V4 UD3_TXD
J8_RXD U4 UD3_RXD
J2000_RXD L0 UART2_RTS_N
J2000_TXD M8 UART2_CTS_N
J2000_CTSn M1 UART2_TXD
J2000_RTSn P4 UART2_RXD

Note that TXD (1V8) is translated to TXD (3V3). NOT TXD (1V8) <-> RXD (1V8). This means that the jumper from the TK1-SOM should go from it’s TX to RX on the daughterboard for a standard ftdi pinout to work.

Note that GPIOs aren’t actually brought out by the board but they are used by the CAN controller (diagram below).

PIN BALL PERIPHERAL ID
TK1_GPIO0 AF29 GPIO3_PS.05
TK1_GPIO1 AA26 GPIO3_PT.00
TK1_GPIO2 AC30 GPIO3_PS.06
TK1_GPIO3 AA31 GPIO3_PS.02
TK1_GPIO4 V28 GPIO3_PS.03
TK1_GPIO5 W31 GPIO3_PR.00
TK1_GPIO6 AB31 GPIO3_PR.06
TK1_GPIO7 Y27 GPIO3_PS.04

CAN Controller (MCP25625) GPIO Usage:

MCP25625 pinout

Construction Information

Schematic canboard_v3.pdf
PCB Sources Repository https://bitbucket.csiro.au/projects/OH/repos/tk1som-can-daughterboard
Gerber Files (in repo also) Tegra_CANboard_tofab_v1.zip
BOM (in repo also) CanBoardBOMDraft1.xlsx

Construction notes

Components R6, R14, R19, R23 should NOT be mounted. R6 and R19 are pull-up resistors that were found to cause signal integrity issues, the other 2 resistors when mounted will supply 5v to the CAN lines and are optional.