topic Re: CAN help on the S08DZ60 in 8-bit Microcontrollers

CAN help on the S08DZ60

meiermat — Thu, 08 Mar 2012 08:02:43 GMT

Hello,

I'm having trouble with getting the MSCAN to transmit a message on the MC9S08DZ60. I have, I think, properly initialized everything, and wrote a subroutine that gets called every 5ms from a timer interrupt. I know the subroutine gets called, because I toggle a pin, and I can set a breakpoint. Unfortunately, the CANTX pin never responds. Right now, the pin is floating. If I connect it to a CAN network through a transceiver, I get the same result. I've checked my initialization code and transmit code against some other examples, but I'm not seeing any problem. I considered that perhaps my code isn't initializing properly, since I'm not waiting for the INITAK bit to be set, but according to the data sheet this should already be set on startup. Additionally, I can view the initialized registers, and they seem to have the correct values.

Moreover, I understand that transmit buffer 0 might not be available when I enter the subroutine. However, when I step through the program, I can see that buffer 0 is empty every time I enter the subroutine. I'll reinstate the appropriate logic once I can get this operating, but I took it out lest it casue an issue.

I can see that the last step in the subroutine, where I'm supposed to be clearing the CANTFLG, isn't working. I can see the $01 loaded into register A, but when that gets stored in CANTFLG, CANTFLG remains at $07, and I don't see any life on the TXCAN line.

I included my initialization code and the transmit code inline in the post. If anyone wants the whole thing, I can provide that as well. I'm using CodeWarrior V10.1 and the PE Micro USB Multilink Interface standalone probe.

Thanks in advance,

Matt

This is my initialization code:

;Initialize CAN

LDA #$80 ;Enable the CAN peripheral

STA CANCTL1

LDA #$F0 ;Enable normal operation, set clock source to bus clock (8MHz)

STA CANCTL1

LDA #$67 ;Set 7xTq before sample, 8xTq after, for 500kHz bitrate

STA CANBTR1

LDA #$00 ;Clear INITRQ, to enter CAN operation

STA CANCTL0

...and this is the subroutine that, I think, should transmit a message:

;****CAN_TX***********************************************

CAN_TX:

LDA #$01 ;Select transmit buffer 0

STA CANTBSEL

LDA #$32 ;Set CAN ID to $191

STA CANTIDR1

LDA #$20

STA CANTIDR0

LDA #$01 ;Set CAN Message to $0123456789ABCDEF

STA CANTDSR0

LDA #$23

STA CANTDSR1

LDA #$45

STA CANTDSR2

LDA #$67

STA CANTDSR3

LDA #$89

STA CANTDSR4

LDA #$AB

STA CANTDSR5

LDA #$DC

STA CANTDSR6

LDA #$EF

STA CANTDSR7

LDA #$08 ;Eight transmit bytes

STA CANTDLR

LDA #$01 ;Clear transmit flag 0

STA CANTFLG

LDA PTFD

EOR #$08

STA PTFD

RTS

;****END CAN_TX***********************************************

Re: CAN help on the S08DZ60

kef — Thu, 08 Mar 2012 13:15:05 GMT

Buy using mysterios constants, and avoiding decent comments in your code, yur are creating problems not only for yourself, but also for others.

Go decifier what $F0 really means below, write decent comment and you will find main reason why it is not working.

LDA #$F0 ;Enable normal operation, set clock source to bus clock (8MHz)

STA CANCTL1

I ignored the rest of code

Re: CAN help on the S08DZ60

meiermat — Thu, 08 Mar 2012 18:50:51 GMT

I apologize. I forget sometimes that most people don't like translating hexadecimal until I leave my desk. I added more complete comments. Hopefully this will help:

;Initialize CAN

LDA #$80 ;%1000 0000 Enable the CAN peripheral by setting CANE bit

STA CANCTL1

LDA #$F0 ;%1111 0000 Enable normal operation by setting LOOPB and LISTEN, set clock source to bus clock (8MHz) by setting CLKSRC, and write CANE to 1 (although this should still have no effect at this point)

STA CANCTL1

LDA #$67 ;%0110 0111 Set 7xTq before sample by loading 7 into TSEG2, 8xTq after sample by loading 8 into TSEG1. This give a 500kHz bitrate

STA CANBTR1

LDA #$00 ;%0000 0000 Clear INITRQ, to enter CAN operation

STA CANCTL0

...and this is the subroutine that, I think, should transmit a message:

;****CAN_TX***********************************************

CAN_TX:

LDA #$01 ;%0000 0001 Select transmit buffer 0 by setting bit 0

STA CANTBSEL

LDA #$32 ;%0011 0010 Set CAN ID to $191 (combine with CANTIDR0)

STA CANTIDR1

LDA #$20 ;%0010 0000 bottom three bits for CAN ID, clear RTR for Data Frame, clear IDE for standard identifiers

STA CANTIDR0

LDA #$01 ;Set CAN Message to $0123456789ABCDEF (CANTDSR0-7)

STA CANTDSR0

LDA #$23

STA CANTDSR1

LDA #$45

STA CANTDSR2

LDA #$67

STA CANTDSR3

LDA #$89

STA CANTDSR4

LDA #$AB

STA CANTDSR5

LDA #$DC

STA CANTDSR6

LDA #$EF

STA CANTDSR7

LDA #$08 ;%0000 1000 Eight transmit bytes

STA CANTDLR

LDA #$01 ;%0000 0001 Clear transmit flag 0 by writing a 1 to TX0

STA CANTFLG

;Toggle a pin to synch with scope, also to verify that the subroutine is being called properly

LDA PTFD

EOR #$08

STA PTFD

RTS ;Return from subroutine

;****END CAN_TX***********************************************

Re: CAN help on the S08DZ60

kef — Thu, 08 Mar 2012 19:23:02 GMT

I forget sometimes that most people don't like translating hexadecimal until I leave my desk.

Wrong conclusion. Hex<->bin, and even hex<->dec is fine for me. Not fine is looking into datasheet how is the meaning of bit 6 is some register. Do you remember them? Certainly you should comment what bits (by name) you are accessing, at least when you are showing your problematic code to someone else than you.

LDA #$F0 ;%1111 0000 Enable normal operation by setting LOOPB and LISTEN, set clock
source to bus clock (8MHz) by setting CLKSRC, and write CANE to 1 (although this should still
have no effect at this point)

Comment still is wrong. Setting LOOPB and LISTEN can't be called normal operation. I had a hope that you will read what does LISTEN mean. You can't have anything transferred with this bit set. Reading Bosch CAN specs could help you a lot.

In TX routine, CANTIDR1 and CANTIDR0 seem being swapped.

Re: CAN help on the S08DZ60

meiermat — Thu, 08 Mar 2012 20:56:58 GMT

I have the Bosch spec. It is, indeed, very helpful. I thought I had "remembered" reading a training document from Freescale that setting both LOOPB and LISTEN would enter normal operation. Apparently I misread it the first several times. Now I'm clearing them both (setting CANCTL1 to $C0), and I'm getting transmission.

You're right about IDR1 and IDR0 being swapped.

Thanks again for the help.

Matt