canusb

CANUSB-PARALLEL

This uses the FTDI UM245R module.

The circuit diagram is http://mergcbus.svn.sourceforge.net/viewvc/mergcbus/trunk/Documents/canusb/CAN_USB3_sch.pdf

The pcb layout is http://mergcbus.svn.sourceforge.net/viewvc/mergcbus/trunk/Documents/canusb/can_usb3_pcb.pdf

CAN_USB3 uses a ready constructed USB interface module (FTDI UM245R) which plugs into a conventional IC socket. This is a reasonably priced module and avoids the need for SM soldering and sourcing of components like the USB B socket.

On the UM245R module, leave the jumper J1 between pins 2 and 3 but remove jumper J2. For more information, download the datasheet from http://www.ftdichip.com/Products/EvaluationKits/UM245R.htm

Power supply

The CAN-USB is a basic node which requires an external 5 volt supply on the two way terminal block (J1) or can be powered from the CBUS terminal block (J2). It should not be powered using both at the same time. The 5V may be taken from other CBUS modules via the CBUS connector pins 1 and 4 or supplied directly to the two pin terminal block on the board. When such an external 5 volt supply is used, it may be connected to the CBUS terminal bock for use by other modules by fitting a link across R1 on the PCB and also the small link above J1. Pads are available for this. Care must be taken not to fit this latter link if the CBUS is already powered from other modules or it will result in two 5 volt supplies being wired in parallel.

For a quick test you can leave temporarily leave the UM245R J2 in place and connect another un-powered module, eg CANACE8C and supply both from a full power (500mA) USB connection. Remember to remove J2 after the test. Unfortunately, in normal use the CAN_USB3 module cannot be reliably powered from the USB cable. On some PC's (laptops etc) the power saving features disconnect power if there has been no activity for a preset time. When used for monitoring traffic on the CBUS, the data from the USB module can not wake up the PC.

The USB interface

The connection is via a standard A to B USB cable. Provided the USB driver has been installed, the PC will automatically detect the CAN_USB module when it is connected. However, the CAN_USB3 module must be powered before the PC will recognise it. It also needs to be powered while installing the VCOM drivers. The port speed of the virtual com port can be set to any rate, as its not actually used with the parallel module. The CAN-USB module, when used with suitable PC software, is fast enough to stream CAN frames at the full rate. It is able to act as a true sniffer without missing any CAN frames.