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03/19/11 19:58
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 		 #181612 - Getting a MAX521 to work with AT89S52
Hi,

I am trying to get a MAX521 to work with a AT89S52 through I2C using bit banging. The microcontroller is running @11.0592Mhz. Port P1.0 is connected to I2C clock and Port P1.1 is connected to I2C Data. I have used 10k external pullups. MAX521 A0, A1 are tied to ground. VREF for the MAX521 is being generated through a LM1117 and is set at 5V. As of now there is nothing connected to any of the DAC outputs.

My code is as below

Save filename.txt
PORT_DAC_CLOCK		EQU	P1.0
PORT_DAC_DATA		EQU	P1.1
LED_RED			EQU	P1.7

DAC_TEST:
;RESET THE DEVICE
	CALL	DAC_START_BIT
	MOV	A,#01010000B
	CALL	DAC_BYTE
	MOV	A,#00010000B
	CALL	DAC_BYTE
	CALL	DAC_STOP_BIT
	CALL	SEC1D			;1 SEC DELAY
	CALL	SEC1D			;1 SEC DELAY
;PUT OUT HALF VOLTAGE AT DAC 7
	CALL	DAC_START_BIT
	MOV	A,#01010000B		;DEVICE ADDRESS
	CALL	DAC_BYTE
	MOV	A,#07H			;DAC ADDRESS
	CALL	DAC_BYTE
	MOV	A,#07FH		;DAC DATA FOR HALF VOLTAGE
	CALL	DAC_BYTE
	CALL	DAC_STOP_BIT	
DONE_DAC_TEST:
	RET

DAC_START_BIT:
	SETB	PORT_DAC_CLOCK	
	SETB	PORT_DAC_DATA
	CALL 	DAC_DELAY
	CLR	PORT_DAC_DATA
	CALL 	DAC_DELAY
	CLR	PORT_DAC_CLOCK
	CALL 	DAC_DELAY
	RET

DAC_STOP_BIT:
	SETB	PORT_DAC_CLOCK
	CALL 	DAC_DELAY
	CLR	PORT_DAC_DATA
	CALL 	DAC_DELAY
	SETB	PORT_DAC_DATA
	CALL 	DAC_DELAY
	RET

DAC_BYTE:
	MOV	R0,#8H
DACB_LOOP:
	RLC	A
	MOV	PORT_DAC_DATA,C
	CALL 	DAC_DELAY		
	SETB	PORT_DAC_CLOCK
	CALL 	DAC_DELAY
	CLR	PORT_DAC_CLOCK
	CALL 	DAC_DELAY
	DJNZ	R0,DACB_LOOP

	SETB	PORT_DAC_DATA
	CALL 	DAC_DELAY
	SETB	PORT_DAC_CLOCK
	CALL 	DAC_DELAY
	JNB	PORT_DAC_DATA,DONE_DAC_BYTE
DAC_NO_ACK:
;TEMPORARY FOR DEBUGGING – FLASH LED TO INDICATE NO ACK FROM MAX521
	CLR	LED_RED
	CALL	SEC1D
	CALL	SEC1D
	SETB	LED_RED
	CALL	SEC1D
	CALL	SEC1D
	SJMP	DAC_NO_ACK
DONE_DAC_BYTE:
	CLR	PORT_DAC_CLOCK
	CALL 	DAC_DELAY
	RET

DAC_DELAY:
	NOP
	NOP
	NOP
	NOP
	NOP
	NOP
	NOP
	NOP
	NOP
	NOP
	NOP
	NOP
	RET

 


I don't get any output at any of the DAC pins. So far I have tried playing around with the I2C timings, resetting the MAX521, changing the MAX521 IC, using DAC 0 to 6, still no output from the DAC. I think the I2C part of things is okay as the MAX521 gives the ACK.

What am I missing? Any pointers / suggestions / feedback is mot welcome.

Warm regards
Punit



List of 8 messages in thread
TopicAuthorDate
Getting a MAX521 to work with AT89S52            01/01/70 00:00      
   Open-collector or open-drain!            01/01/70 00:00      
      Quasi bidirectional            01/01/70 00:00      
      Tried port 0            01/01/70 00:00      
   Checked these things?            01/01/70 00:00      
      Tried these as well            01/01/70 00:00      
         Is the micro running at all?            01/01/70 00:00      
            Solved!!!            01/01/70 00:00      

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