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I'm attempting to get CAN running on a 56F8323, but I'm having issues with the CANTx pin.

The rise time of the CANTx pin is extremely slow, and the fall time is fine, almost as if the pin is drifting high and being driven low. I am using 1Mbit CAN, so the bit time is 1uS, but the rise time is also 1uS.

I have tried both settings for the pin in the GPIOC_PPMODE (Push-Pull Output Mode Control) register, but it does not appear to affect the output behaviour when the pin is used for CAN.

I have tried both settings for the pin in the GPIOC_PUR (Pull-up Enable) register, but the rise time is even worse when the pullup is disabled for the pin.

Our circuit follows the examples in various datasheets, with the CANTx and CANRx connected directly to the CAN tranceiver (SN65HVD233D). I have also tried the code on the 56F8300DEMO board with the same results.

I have also tried the CAN bootloader code supplied by Freescale, and have observed the same slow rise times on CANTx.

Has anybody got CAN running on the 56F8323, and were there any tricks?





(You need to be a member of motoroladsp -- send a blank email to motoroladsp-subscribe@yahoogroups.com )

Hi James

You might consider trying a 1 K Ohm external pull-up to +5V on CAN_TX.

I see in the Tech Data sheet for the 568357, Table 2-2, that CAN_RX has an
internal pull-up (value not specified). However, for that chip, NO internal
pull-up is shown for CAN_TX! It is listed as an open-drain output, I'm not
sure how many mA. Since this is also a "FlexCAN" peripheral, your chip may
have the same situation.

In the same doc, Section 6.5.6.3 calls out Bit 13 of SIM_PUDR to control the
pull-up on CAN_RX (nothing said about any pull-up for CAN_TX).

Good luck to you, and please let us know how it turns out.

Rick Corey

-----Original Message-----
From: jackson.james@jack... [mailto:jackson.james@jack...]
Sent: Wednesday, April 13, 2005 2:46 AM
To: motoroladsp@moto...
Subject: [motoroladsp] CANTx pin behaviour in FlexCAN (56F8323)
I'm attempting to get CAN running on a 56F8323, but I'm having issues with
the CANTx pin.

The rise time of the CANTx pin is extremely slow, and the fall time is fine,
almost as if the pin is drifting high and being driven low. I am using 1Mbit
CAN, so the bit time is 1uS, but the rise time is also 1uS.

I have tried both settings for the pin in the GPIOC_PPMODE (Push-Pull Output
Mode Control) register, but it does not appear to affect the output
behaviour when the pin is used for CAN.

I have tried both settings for the pin in the GPIOC_PUR (Pull-up Enable)
register, but the rise time is even worse when the pullup is disabled for
the pin.

Our circuit follows the examples in various datasheets, with the CANTx and
CANRx connected directly to the CAN tranceiver (SN65HVD233D). I have also
tried the code on the 56F8300DEMO board with the same results.

I have also tried the CAN bootloader code supplied by Freescale, and have
observed the same slow rise times on CANTx.

Has anybody got CAN running on the 56F8323, and were there any tricks?



(You need to be a member of motoroladsp -- send a blank email to motoroladsp-subscribe@yahoogroups.com )

Hi!

I have the same experience as Rick using a 568536 and I use a 1k pull up for the CAN_TX pin. Works great.

Best Regards,

Rikard

-----Original Message-----
From: jackson.james@jack...
To: motoroladsp@moto...
Date: Wed, 13 Apr 2005 02:45:57 -0400
Subject: [motoroladsp] CANTx pin behaviour in FlexCAN (56F8323) I'm attempting to get CAN running on a 56F8323, but I'm having issues with the CANTx pin.

The rise time of the CANTx pin is extremely slow, and the fall time is fine, almost as if the pin is drifting high and being driven low. I am using 1Mbit CAN, so the bit time is 1uS, but the rise time is also 1uS.

I have tried both settings for the pin in the GPIOC_PPMODE (Push-Pull Output Mode Control) register, but it does not appear to affect the output behaviour when the pin is used for CAN.

I have tried both settings for the pin in the GPIOC_PUR (Pull-up Enable) register, but the rise time is even worse when the pullup is disabled for the pin.

Our circuit follows the examples in various datasheets, with the CANTx and CANRx connected directly to the CAN tranceiver (SN65HVD233D). I have also tried the code on the 56F8300DEMO board with the same results.

I have also tried the CAN bootloader code supplied by Freescale, and have observed the same slow rise times on CANTx.

Has anybody got CAN running on the 56F8323, and were there any tricks?




(You need to be a member of motoroladsp -- send a blank email to motoroladsp-subscribe@yahoogroups.com )