HS mode 20Mhz, irregular values when reading/writing to regi

[trean]

When using 18F258 with 20Mhz crystal and HS mode (No PLL) I cannot write to register without putting a delay between writes.

Example:

#byte CANCON = 0xf6f
#byte RXM1EIDL = 0xf1f
#byte RXM1EIDH = 0xf1e
#byte RXM1SIDL = 0xf1d
#byte RXM1SIDH = 0xf1c
#byte RXM0EIDL = 0xf1b
#byte RXM0EIDH = 0xf1a
#byte RXM0SIDL = 0xf19
#byte RXM0SIDH = 0xf18


void main( void ) {

CANCON = 0x80; //Set configuration mode
RXM0SIDH = xx; // write any values to registers
RXM0SIDL = yy;

printf( "\%2x, \%2x\r", RXM0SIDH,RXMOSIDL );
CANCON = 0x00; // return to normal mode

The printf command will not return xx and yy but a fixed other value.
if I insert a delay_ms(1) (1ms has no relevance, could be less, don't know exactly how much less...) between each of the register writes the code will return the correct values.

The above is just a code extraction, the real code is much bigger but the effect is the same. A short delay between writes makes it all work.

Can anyone enlighten me to why it acts like this ????
( PCWH 3.128 )

Best wishes
___________________________
This message was ported from CCS's old forum
Original Post ID: 9807

[trean]

Oh well...

I respone to myself I must admit to not reading the datasheet closely enough.

After changing operation mode you must monitor the opmode bits before accessing the registers.

I did not delete my originalpost since I thought that this may be of help to someone in the future when they search this board.
(Which I do alot...)
___________________________
This message was ported from CCS's old forum
Original Post ID: 9810