It sounds like you have a problem connecting the MAX485 to a PIC?  Make sure that when you set the PIC to Tx that you give it a few uSecs to settle before sending the instruction packet.

Also the instruction packet signature in your post might not be correct. All arguments passed to the Dynamixel bus are bytes.  If you have a 2 byte piece of data you must send it low-high byte.  Check your code and connections.

Thanks MikeG for your comment

Actually I am controling the time to send instructions by the delay routine

;********************************************************************************************
;Tx_Dato: Transmite vía serie el dato presente en el reg. W
;*************************************************************************************
Tx_Dato            bcf        PIR1,TXIF             ; Restore the flag of transmisor
                          movwf        TXREG            ; Save the byte to transmit
                           bsf        STATUS,RP0
Tx_Dato_Wait    btfss        TXSTA,TRMT    ;Byte send??
                          goto        Tx_Dato_Wait;   No, wait
                          bcf        STATUS,RP0
                           return                    ; YES 

And I am thinking that the connection betwen the Max232 and the Max485 could have problems in the reference voltage or impedance(?) I was found three or four diferents ways to mount this connection... and i'ts very dangerous

If someone else have any experience or idea about, it will be wellcome

many thanks again!

I'm using a SN65176B which is pin compatible with the MAX485.  What's the MAX232 for?  What are you doing with RO, RE, DE, and DI pins?  You might want to take a look at the RS485 datasheet.

Anyway, when I switch directions with the SN65176B I have to add a few uSec of delay due to the speed of my uController. 

Joan,

Looks like you may have made the wrong circuit or improperly controlled the 485 port.

For examples, please refer to the Dynamixel SDK platform porting found in the Tech Support.

http://support.robotis.com/en/techsupport_eng.htm#software/dynamixel_sdk/sourcestructure.htm

ROBOTIS