Domino Application Notes

	AN501
	Product: Domino 1 and 2
Adding an External DAC	Date: 3/6/98
Introduction: This application note shows how to interface a 12-bit serial digital to analog converter to the Domino 1 and 2.
Background: Even though the Domino modules offer a wide range of features, sometimes you need a little something extra like a DAC output. Connecting a serial device such as the Linear Technologies LTC1257 DAC can be accomplished easily with a few lines of BASIC code and three bits of Port 1.
How it works: The sample program asks the user for the desired output voltage of the LTC1257’s output pin and outputs the desired voltage. If additional outputs are needed, the clock and data lines may be shared between devices and additional Port 1 pins used to select the individual chips.
Program Listing: 10 REM Domino - LTC1257 DAC Program 20 REM LD = Port1.4, CLK = Port1.5, DIN = Port1.6 30 LD = 10h : CK = 20h : DA = 40h 40 PORT1 = PORT1 .OR. LD : REM raise LD 50 PORT1 = PORT1 .AND. (0FFh-CK) : REM drop CLK 60 PORT1 = PORT1 .AND. (0FFh-DA) : REM drop DIN 70 INPUT "Enter desired output voltage: ",V 80 V = V/(5/4095) 90 FOR X = 11 TO 0 STEP -1 95 REM TEST VALUE, IF BIT=1 THEN CLOCK A 1, ELSE CLOCK A 0 100 IF (V.AND.2*X)<>0 THEN GOSUB 2000 ELSE GOSUB 1000 110 NEXT X 120 GOSUB 3000 130 PRINT 140 GOTO 70 1000 PORT1 = PORT1 .AND. (0FFh-CK) : REM drop CLK 1010 PORT1 = PORT1 .AND. (0FFh-DA) : REM drop Din 1020 PORT1 = PORT1 .OR. CK : REM raise CLK 1030 RETURN 2000 PORT1 = PORT1 .AND. (0FFh-CK) : REM drop CLK 2010 PORT1 = PORT1 .OR. DA : REM raise Din 2020 PORT1 = PORT1 .OR. CK : REM raise CLK 2030 RETURN 3000 PORT1 = PORT1 .AND. (0FFh-LD) : REM drop LD 3010 PORT1 = PORT1 .OR. LD : REM raise *LD 3020 RETURN