AD9850 DDS code

[cunninghamjohn]

I have bought a cheap DDS module from CHina and want to start by producing a fixed output of 500kHz, there is no LCD or rotary encoder as yet; This is my code:

include "modedefs.bas"
pause 1000; allow circuit 1 sec to stabilise
pulsout porta.0,100;pulse reset pin
pause 20
pulsout porta.3,100;Pulse w_clk
pause 20
pulsout porta.2,100;pulse fq_ud to set up serial data mode
pause 20

shiftout porta.1,porta.3,0,[%10111000];send out tuning word 1 w0-w7
;porta.1 is data, porta.3 is W_CLK

shiftout porta.1,porta.3,0,[%00100100];send out tuning word 2 w8-w15

shiftout porta.1,porta.3,0,[%01100000];send out tuning word 3 w16-w23

shiftout porta.1,porta.3,0,[%10000000];send out tuning word 4 w24-w31

shiftout porta.1,porta.3,0,[%00000000];send out tuning word 5 w32-w39
pause 10
pulsout porta.2,100; pulse FQ_UD on data complete, update DDS
high portb.4
pause 2000
low portb.4;flash LED on portb.4 for 2 secs to show data sent
end

Needless to say, it wont work. I have also hardwired D0 and D1 to +Vdd and D2 to GND to force serial mode. Any advice?

John

[Ioannis]

Did you remembered to make all port A digital? Normally Port A defaults to Analog or Comparator.

Ioannis

[HenrikOlsson]

Hi,
I've only looked briefly at your code but I think your tuning value is wrong.
For 500kHz you want 500k*2^32/125M = $01 06 24 DD. You're sending $80 60 24 B8 which would equal a frequency way above 60Mhz....

Try

SHIFTOUT PortA.1, PortA.3, 0, [$DD, $24, $06, $01, $00]

Also, which PIC are you using? PortA usually contains analog functions which needs to be disabled for the pins to work in digital mode. I don't see that in your code.

Finaly, when you force serial mode thru the hardware there's no need to do anything else at the startup - atleast I didn't have to. Perhaps your startup code is locking up the AD9850.

/Henrik.

[cunninghamjohn]

Thanks for the replies on the matter.

Did you remembered to make all port A digital? Normally Port A defaults to Analog or Comparator.

Im using a 16F628, I thought the SHIFTOUT command automatically made the named ports digital outputs, but will insert a line of code as you suggest.

I've only looked briefly at your code but I think your tuning value is wrong

Yes you are right, will change the values and see what happens.

Finaly, when you force serial mode thru the hardware there's no need to do anything else at the startup

Thanks for that clarification

[cunninghamjohn]

This is the latest code. Gave up on the SEROUT command and tryed the following so that i could slow down the sequence and see LEDs representing the signals. Cannot get anything out of the AD9850 still. I know the DDS module works as I proved it with someone elses software.

trisb=$0;SET ALL OF PORTB TO OUTPUTS

RESET VAR PORTB.7
CLOCK VAR PORTB.6
DATAPIN VAR PORTB.5
DONE VAR PORTB.4;DEFINE
P VAR WORD;WIDTH OF DATA PULSE
P=50
Q VAR WORD;PAUSE BETWEEN DATA BITS
Q=10
R VAR WORD;PAUSE BETWEEN DATA WORDS
R=30
W VAR BYTE;VARIABLE REPRESENTING BYTES 0 TO 5
W0 VAR BYTE;WORD 0
W1 VAR BYTE;WORD 1
W2 VAR BYTE;WORD.2
W3 VAR BYTE;WORD.3
W4 VAR BYTE;WORD 5

;DATA FOR BINARY WORDS
W0=$DD;WORD 0 HEX
W1=$24;WORD 1 HEX
W2=$06;WORD 2 HEW
W3=$01;WORD 3 HEX
W4=$00;WORD 4 HEX

PORTB=$00; SET ALL PINS LOW
MAIN:
PAUSE 2000
HIGH RESET
PAUSE P
LOW RESET; PULSE RESET PIN
PAUSE R
W=W0
GOSUB BYTEOUT

PAUSE R
W=W1
GOSUB BYTEOUT

PAUSE R
W=W2
GOSUB BYTEOUT

PAUSE R
W=W3
GOSUB BYTEOUT

PAUSE R
W=W4
GOSUB BYTEOUT

PAUSE R
PULSOUT DONE,3000; ALL 40 BITS SENT

HIGH RESET; REPEAT SEQUENCE AGAIN
PAUSE P
LOW RESET; PULSE RESET PIN
W=W0
GOSUB BYTEOUT
PAUSE R
W=W1
GOSUB BYTEOUT
PAUSE R
W=W2
GOSUB BYTEOUT
PAUSE R
W=W3
GOSUB BYTEOUT
PAUSE R
W=W4
GOSUB BYTEOUT
PAUSE R
PULSOUT DONE,3000; ALL 40 BITS SENT
END

BYTEOUT:;SUBROUTINE TO CLOCK OUT BITS 0 TO 7 OF BINARY WORD W

PAUSE P
DATAPIN=W.BIT0
PAUSE 20
HIGH CLOCK
PAUSE P
LOW CLOCK
PAUSE 20
LOW DATAPIN; CLOCK OUT BIT0

PAUSE Q
DATAPIN=W.BIT1
PAUSE 2
HIGH CLOCK
PAUSE P
LOW CLOCK
PAUSE 2
LOW DATAPIN; CLOCK OUT BIT1

PAUSE Q
DATAPIN=W.BIT2
PAUSE 2
HIGH CLOCK
PAUSE P
LOW CLOCK
PAUSE 2
LOW DATAPIN; CLOCK OUT BIT2

PAUSE Q
DATAPIN=W.BIT3
PAUSE 2
HIGH CLOCK
PAUSE P
LOW CLOCK
PAUSE 2
LOW DATAPIN; CLOCK OUT BIT3

PAUSE Q
DATAPIN=W.BIT4
PAUSE 2
HIGH CLOCK
PAUSE P
LOW CLOCK
PAUSE 2
LOW DATAPIN; CLOCK OUT BIT4

PAUSE Q
DATAPIN=W.BIT5
PAUSE 2
HIGH CLOCK
PAUSE P
LOW CLOCK
PAUSE 2
LOW DATAPIN; CLOCK OUT BIT5

PAUSE Q
DATAPIN=W.BIT6
PAUSE 2
HIGH CLOCK
PAUSE P
LOW CLOCK
PAUSE 2
LOW DATAPIN; CLOCK OUT BIT6

PAUSE Q
DATAPIN=W.BIT7
PAUSE 2
HIGH CLOCK
PAUSE P
LOW CLOCK
PAUSE 2
LOW DATAPIN; CLOCK OUT BIT7
PAUSE Q
RETURN

[HenrikOlsson]

Hi,
Sorry for the late reply, you've probably figured it out by now.
But in case you haven't, have you verified that your PIC is actually running?
I've just tried the following code here, all wired up on a breadboard using a 16F628 using a 4MHz x-tal and a AD9850 module, compiled with PBP 3.0.6.4. Module forced into serial mode by tying D0,D1 high and D2 low. It outputs a 500kHz signal as expected:

DEFINE OSC 4

Clk VAR PortB.5                 ' Clock output pin
Dta VAR PortB.6                 ' Data output pin
FUd VAR PortB.7                 ' Frequency update output pin

PortB = 0
TRISB = 0                       ' All outputs

Pause 1000                      ' Let everything power up

' Tuning word for 500kHz = 500000*2^32/125000000 = 17179869 or, in HEX, $010624DD
' The AD9850 wants the least significant byte first:
SHIFTOUT Dta, Clk, 0, [$DD, $24, $06, $01, $00]

' Now pulse the Frequency update pin
FUd = 1 : PauseUS 10 : FUd = 0

' Blink a LED to show we're alive.
Done:
  Toggle PortB.3
  Pause 100
Goto Done

Here's the result:


/Henrik.

[HenrikOlsson]

Just a follow up to the previous post.
For reference, here's the "schematic" for the setup I used with the above code. There are a couple of different modules in circulation so make sure the actual signals and not the pin numbers matches your particular module.



If you're programming the PIC in-circuit perhaps the programmer is loading RB6, RB7 (since they are the programming pins) preventing them from operating the AD9850 properly? I'm doing just that with a PICKit3 on my breadboard and don't see any issues but it's a thought.

/Henrik.