DSPIC33EP128GP506 CAN BAUD RATE

georpo · Joined: 18 Nov 2008 Posts: 278 Location: Athens, Greece.

Hello,

I am using a DSPIC33EP128GP506 with MCP2551.

Ttelmah · Joined: 11 Mar 2010 Posts: 19231

Do what everyone else does. Use one of the online calculators.
Standard way is to use one, then sit down and do one set of calculations
yourself to be 'happy' with the values you are being given.
So (for example):
[url]
http://www.bittiming.can-wiki.info/
[/url]
Select the PIC33 as the processor type, and go from there.

georpo · Joined: 18 Nov 2008 Posts: 278 Location: Athens, Greece.

Ttelmah thanks for the reply.
No matter what settings, the microchip can bus analyzer tool says "error passive" "TX ERR:128"
_________________
George.

temtronic · Posted: Thu Jan 25, 2024 6:05 am

curious was I.
googled this ... microchip can bus analyzer tool says "error passive" "TX ERR:128"

found this

https://e2e.ti.com/support/microcontrollers/c2000-microcontrollers-group/c2000/f/c2000-microcontrollers-forum/978244/launchxl-f280049c-can-bus-external-transmit-node-not-recognized

maybe will help ??

I have no idea what ERR:128 is, hopefully there's a 'list of error messages' somewhere....

georpo · Joined: 18 Nov 2008 Posts: 278 Location: Athens, Greece.

it just means that there is no ACK from the other side.
I have the microchip analyzer sending data at 250k verified at the oscilloscope and on the mcp2551 data pin but my dspic never receives. on the other hand I can not set the baud rate values right.

maybe just give up and use mcp2515
_________________
George.

Ttelmah · Joined: 11 Mar 2010 Posts: 19231

The MCP4551 transceiver is a 5v device. Your PIC is a 3.3v device.
Not surprising it doesn't work.

georpo · Joined: 18 Nov 2008 Posts: 278 Location: Athens, Greece.

Ttelmah,
I know that but the mcp2551 data out is connected to a 5v tolerant pin of the dspic.
I have done this before, I do not think this is the problem. Do you? should I add a voltage divider?
_________________
George.

Ttelmah · Joined: 11 Mar 2010 Posts: 19231

Seriously, look at MicroChip's own note on this:

[url]
https://microchip.my.site.com/s/article/CAN-transceiver-for-3-3V-microcontrollers
[/url]

georpo · Joined: 18 Nov 2008 Posts: 278 Location: Athens, Greece.

I have used many many times USB-TTL adapters that are 5V directly to UART '5v tolerant" RX pins with no problem.

OK, I will just add 2 resistors and see how it goes.
_________________
George.

gaugeguy · Joined: 05 Apr 2011 Posts: 289

Are you also planning to resistively divide the PIC output voltage higher?
It is a high speed bus, so should be done correctly.

Ttelmah · Joined: 11 Mar 2010 Posts: 19231

Remember also that Fcan, is not the Fcpu. It is the Fp (peripheral clock), or
this *2. Depends on CANCKS.

I'm more worried about whether the output from the 3.3v device is
reliably seen as Vih on the transceiver. All too common that this is not
the case, and this would give a bus that will not correctly signal the dominant
phase.

I too have used the Texas transceivers mentioned below.

The symptoms you have are of the bus not correctly being driven...

gaugeguy · Joined: 05 Apr 2011 Posts: 289

For 3.3V processors I have personally used both the TJA1042T/3 and SN65HVD230D

georpo · Joined: 18 Nov 2008 Posts: 278 Location: Athens, Greece.

I just used a completely different example "EX_CAN_CCS_A_PCD.C"
compiled ok, no reception on th pic.

I will try 1k/2k resistors and order some MCP2562
_________________
George.