AD9850 interfaced with PIC16F877A

ad9850

hey, anybody here who can help me build a schematic design in interfacing an Analog IC AD9850 to a PIC16F877A.. I really am having difficulties on the biasing/connecting the AD9850 as well as other components that the AD9850 might need to function properly..

I'm a newbie in this hobby.. I'm planning to build a signal generator with the AD9850 controlled by the PIC16F877A.. i have yet no problems with the PIC16F877A circiutry.. if all goes well, i will add a keypad as input to the PIC and hav an LCD display still interfaced with the PIC..

I know PIC16F877A is large and good enough to handle this..

ad9850 pic

A Google search give me a ton of hits. Maybe you'll find something useful:
http://www.google.com/search?as_q=AD9850+pic

Here's an article from July 1997 QEX magazine, "Building a Direct Digital Synthesis VFO". It uses an AD9850 and PIC16C54. The link will self-destruct soon.
**broken link removed**

qex magazine

Here's an article from July 1997 QEX magazine, "Building a Direct Digital Synthesis VFO". It uses an AD9850 and PIC16C54. The link will self-destruct soon.
h**p://s4.yousendit.com/d.aspx?id=387NQ4FAOE3GG0T1IIHIPBJE2A

what is the function of the rotary encoder? Is it used as input to the PIC and and thereby changing the 32-bit tuning word to the ad9850?

can i use a keypad instead?

ad9850 datasheet

See the paragraph under "Project Description". This VFO is used in a radio receiver, so the encoder is the tuning knob. Yes you can replace it with a keypad.

ad9850 pic serial

Question#1:
From the datasheet of AD9850, it says that a square wave can be produced using the AD9850 high-speed comparator. How are we going to implement this? The projects i found in the internet all didn't use this feature of AD9850.

Question#2:
The data can be loaded to AD9850 via serial method or parallel loading method. Which is better (advantages/disadvantage)? All projects in the internet, again, are using serial loading method instead of parallel method. I'm planning to use parallel loading method. Am I just gonna be using the same connections and components used in serail loading?

Question#3:
Again, the projects i found in the internet are using the Canned Oscillator Module type of crystal oscillator. I found out that this type is not available in electronics shop here in our city. Any ideas on alternatives?

dac interface with pic16f877a

1. Page 13 and 14 of the AD9850 datasheet describes the AD9850/CGPCB evaluation board, which uses the comparator.

2. The parallel interface is faster loading and probably easier to program, but it consumes more pins on your controller. You decide which way is better for your project.

3. Buy an oscillator from a mail-order company (I use DigiKey and Mouser in USA), or remove one from an old discarded computer board. You may not get the exact frequency you want, but the DDS is flexible.

dac interface with pic16f877a

which would be more advisable, to use a higher or a lower frequency for our reference clock in AD9850??? I am aware that lower frequencies would give me a tighter frequency resolution, but, do the reference frequency affect the DAC? i have this weird feeling that using higher ref freq would give me a finer DAC output. i stand to be corrected.. heheh..

we only have this frequencies to choose from: 80MHz, 64MHz, 50MHz or 24MHz. we are only interested in having a maximum output frequency of 1MHz.

ad9850 problem serial

as promised, here's my schematics. It uses rotary optical encoder to change the frequency and two push-buttons to select the desired digit.