TM4C123GH6PM: CAN Bit time calculation.

That is essentially just a repeat of your original post. Not sure how it answers your question but if you are satisfied....

Robert

*** Corrected ***

I have reliable CAN communication at 1M baud with 50MHz system clock using:

    // 50MHz from 16MHz crystal
    SysCtlClockSet(SYSCTL_SYSDIV_4 | SYSCTL_USE_PLL | SYSCTL_OSC_MAIN |
                   SYSCTL_XTAL_16MHZ);

    CANBitRateSet(CAN0_BASE, SysCtlClockGet(), 1000000);

The CAN0 registers are set as shown: *** Corrected ***

Bob Crosby said:

// 50MHz from 16MHz crystal

SysCtlClockSet(SYSCTL_SYSDIV_8 | SYSCTL_USE_PLL | SYSCTL_OSC_MAIN | SYSCTL_XTAL_16MHZ);

Might that  "50MHz from 16MHz crystal"  result (instead) from, "SYSCTL_SYSDIV_4"?

TM4C123 runs PLL @ 200MHz (iirc) - thus the divide is 4.

CB1, as always thank you for double checking me. I pulled this table from page 1374 of the data sheet which shows the PLL at 400Mhz. The CAN worked correctly at 1MBaud (connected to a NI USB CAN module) which implies that I really was operating at 50MHz using SYSCTL_SYSDIV_8.

Bob Crosby said:

CB1, I should never question your corrections.

Bob - we both realize that - on occasion - even a blind squirrel blunders upon a walnut.      To be "fair" - multiple times I have "Liked" your posts (not just "corrected") - thus there IS a balance.      (although that "like" favor appears not to have been returned...)

Would that gf - unruly sailing crüe - and crack staff  (all) adopt that,  "aversion to question."       (Not a chance...)

Hi Bob Crosby,

I am using 50MHz from 8MHz crystel.

ROM_SysCtlClockSet(SYSCTL_SYSDIV_4 | SYSCTL_USE_PLL | SYSCTL_OSC_MAIN | SYSCTL_XTAL_8MHZ);

and using CANBitTimingSet() library function for Baud Rate.

#define CANBAUD_100K 0
#define CANBAUD_125K 1
#define CANBAUD_250K 2
#define CANBAUD_500K 3
#define CANBAUD_1M    4

CANBitTimingSet(CAN1_BASE,&CANBitClkSettings[CANBAUD_500K]);

tCANBitClkParms CANBitClkSettings[] =
{
{16, 8, 4, 20},    // CANBAUD_100K ok at 50MHz clock.
{13, 2, 4, 25},    // CANBAUD_125K ok at 50MHz clock.
{6, 1, 2, 25} ,     // CANBAUD_250K ok at 50MHz clock.
{16, 3, 2, 5},      // CANBAUD_500K ok at 50MHz clock.
{8, 1, 1, 5}         // CANBAUD_1M ok at 50MHz clock.
};

Could you please help me out, what are the CAN bit timing parameter values to achieve 100k, 125k, 250k, 500k, 800k and 1mbps baud rate for 80MHz system clock from 8MHz crystal. 

Thanks & Regards

Suman 

Suman Soora said:

In my application, i am using 80MHz from 8Mhz crystal.
and CANBitRateSet(CAN1_BASE, SysCtlClockGet(),Baudrate);
Here, for baud rates 100k, 125k, 250k, 500k, getting data from CAN transceiver(SN65HVD1040D) and also i can see the data in PCAN with those baud rates.
But, if baud rate is 800k or 1 mbps, didn't get data from CAN Transceiver and PCAN is showing BUSHEAVY.

My original suggestion/question still stands. And I will add to those, the length of the cable.

You have not provided any reasoning for thinking the original parameters should be modified.

Robert

Robert Adsett said:

Suman Soora

In my application, i am using 80MHz from 8Mhz crystal.
and CANBitRateSet(CAN1_BASE, SysCtlClockGet(),Baudrate);
Here, for baud rates 100k, 125k, 250k, 500k, getting data from CAN transceiver(SN65HVD1040D) and also i can see the data in PCAN with those baud rates.
But, if baud rate is 800k or 1 mbps, didn't get data from CAN Transceiver and PCAN is showing BUSHEAVY.

My original suggestion/question still stands. And I will add to those, the length of the cable.

Let me be a little more explicit

1. What is your transceiver?
2. What are you using for a cable?
3. How long is your cable?
4. How are you terminating the bus?

Robert

His transceiver was listed, "CAN transceiver(SN65HVD1040D)."

All other of your questions (and mine) hold.

In addition - any Freq. error at the (other) end - if in the opposite direction of MCU's error - proves additive - thus the (other) end demands attention too!

Poster's continued "Cut/Pastes" prove not so fruitful - instead real measurements - and direct response to probings - best resolve...

As always - test upon MULTIPLE BOARDS (never just one) avoids "helper abuse" (surely a high poster concern) in diagnosing dreaded, "Single Board Anomalies."

There are several ways to achieve those timings. To make them the same as you have with the 50MHz clock, simply change the pre-scale by 8/5.

	tCANBitClkParms CANBitClkSettings[] =
	{
		{16, 8, 4, 32},    // CANBAUD_100K ok at 80MHz clock.
		{13, 2, 4, 40},    // CANBAUD_125K ok at 80MHz clock.
		{6, 1, 2, 40} ,    // CANBAUD_250K ok at 80MHz clock.
		{16, 3, 2, 8},     // CANBAUD_500K ok at 80MHz clock.
		{8, 1, 1, 8}       // CANBAUD_1M ok at 80MHz clock.
	};

Hi,

In my application, i am using 80MHz from 8Mhz crystal.
and CANBitRateSet(CAN1_BASE, SysCtlClockGet(),Baudrate);
Here, for baud rates 100k, 125k, 250k, 500k, getting data from CAN transceiver(SN65HVD1040D) and also i can see the data in PCAN with those baud rates.
But, if baud rate is 800k or 1 mbps, didn't get data from CAN Transceiver and PCAN is showing BUSHEAVY.

So, Instead of using CANBitRateSet() library function, I decided to use CANBitTimingSet() library function.
Please help me out, what are the CAN bit timing parameter values need to pass through the CANBitTimingSet() to get 100k, 125k, 250k, 500k, 800k and 1Mbps Baud Rate for 80MHz system clock from 8MHz crystal. In data sheet of CAN Transceiver(SN65HVD1040D) is telling that, it supports upto 1 mbps baud rate.

Could you please calculate the CAN Bit timing parameters at 80MHz system clock for above mention baud rates.

As discussed in earlier post,
In stellariware micro controller, I have tried with 50MHz from 8MHz crystal, and using CANBitTimingSet() library with below mentioned CAN Bit clock parameter values, it is working smoothly for 100k, 125k, 250k, 500k and 1Mbps baud rate. I am able see the data in PCAN also.

tCANBitClkParms CANBitClkSettings[] =
{
{16, 8, 4, 20}, // CANBAUD_100K ok at 50MHz clock.
{13, 2, 4, 25}, // CANBAUD_125K ok at 50MHz clock.
{6, 1, 2, 25} , // CANBAUD_250K ok at 50MHz clock.
{16, 3, 2, 5}, // CANBAUD_500K ok at 50MHz clock.
{8, 1, 1, 5} // CANBAUD_1M ok at 50MHz clock.
};
Here,
bit rate = CAN Clock / ((ui32SyncPropPhase1Seg + ui32Phase2Seg + 1) * (ui32QuantumPrescaler)) ;
Based on above CAN bit clock setting parameter values and 50MHz from 8MHz crystel, may i know, what is the value of Propagation segment, Phase 1 segment, phase 2 segment value and total number of quantum (n) value.

Dear Robert,

This is how the hardware interface is:

Manuraj Nambayil said:

This is how the hardware interface is:

There is nothing after this point.

Robert

Suman Soora said:

I am using gridconnect USB/CAN adapter and its length is about 1 meter , connected between hardware and PC.

One metre is good, but that still leaves the questions about termination and cable.

Robert

This is how the hardware interface is:

Look (very) fast folks!

("some" effort (review) required when posting...)       Note that the "empty" hardware interface has (like "LIKE") gone AWOL!      (yet has been (twice now) preserved...)

Thank you for updating the hardware interface

Good Manuraj,

That looks good. What about the other end and what about the cable?

Robert

Hi Robert,

We are using grid connect USB/CAN Adapter device and length of the cable is about 1 meter. And we have been using the same set-up for the past 5 years.

Refer the below snapshot for device and cable.

Your CAN interface schematic is quite good - yet the CAN Xcvr is powered from 5V - not 3V3. Might that alone account for the "fall-off" you note at the highest (i.e. most demanding) CAN Data Rates? (Your MCU outputs 3V3 - which may prove "marginal" for a 5V powered IC - especially at extreme data rates!)

3V3 CAN Xcvrs ARE available - and are likely to "fit" your existing pcb footprint...

CAN pics.zip