hola mis amigos, espero que este 2009 traiga muchos exitos para todos ustedes!!!, una vez mas aprovecho para agredecerles por la ayuda brindada, han sido de mucha ayuda varios temas de esta pag.
hoy me dirijo a uds con una duda, no es tanto de PIC´s, es mas bien de comprension de lectura, les comento:
recien adquiri un DDS de analog devices (AD9913), este dispositivo necesita de una programación previa para poder entregar la frecuencia que el usuario desee, esto se hace configurando un registro llamado FTW (frecuency tuning word); ahora para poder acceder a ese registro se utiliza un byte de instruccion en el cual se debe enviar información de si habra una accion de lectura o escritura y la direccion del registro al que quiero accesar (FTW) . hasta ahi todo bn, el problema ke tengo ahora, es ke cada registro trae consigo 3, 4,5 y hasta 6 bytes y estos traen otras direcciones.
mi pregunta, la mas concreta es; si yo quiero cambiar el dato de un solo bit en el ultimo byte del registro, segun el datasheet, tengo que reescribir todos los bytes del registro??. Alguien ha trabajado con esta belleza de DDS?, como acceso a los bytes del registro???, les dejo un fragmento del datasheet por si alguien se anima a ayudarme, agradezco de antemano la ayuda, byeee
"..There are two phases to a communication cycle with the AD9913. Phase 1 is the instruction cycle, which is the writing of an instruction byte into the AD9913, coincident with the first eight SCLK rising edges. The instruction byte provides the AD9913 serial port controller with information regarding the data transfer cycle, which is Phase 2 of the communication cycle. The Phase 1 instruction byte defines whether the upcoming data transfer is read or write and the serial address of the register being accessed.
The first eight SCLK rising edges of each communication cycle are used to write the instruction byte into the AD9913. The remaining SCLK edges are for Phase 2 of the communication cycle. Phase 2 is the actual data transfer between the AD9913 and the system controller. The number of bytes transferred during Phase 2 of the communication cycle is a function of the register accessed. For example, when accessing the Control Function Register 2, which is two bytes wide, Phase 2 requires that two bytes be transferred. If accessing one of the profile registers, which are six bytes wide, Phase 2 requires that six bytes be transferred. After transferring all data bytes per the instruction, the communication cycle is completed.
At the completion of any communication cycle, the AD9913 serial port controller expects the next eight rising SCLK edges to be the instruction byte of the next communication cycle.
Instruction Byte
The instruction byte contains the following information as shown in the instruction byte bit map.
Instruction Byte Information Bit Map
MSB LSB
D7 D6 D5 D4 D3 D2 D1 D0
R/W X X A4 A3 A2 A1 A0
R/W—Bit 7 of the instruction byte determines whether a read or write data transfer occurs after the instruction byte write. Logic high indicates read operation. Logic 0 indicates a write operation.
X, X—Bit 6 and Bit 5 of the instruction byte are don’t care.
A4, A3, A2, A1, A0—Bit 4, Bit 3, Bit 2, Bit 1, and Bit 0 of the instruction byte determine which register is accessed during the data transfer portion of the communications cycle. .."
muchas gracias p or la colaboracion amigos
