'16-bit PWM Optoisolated DAC is PC-Controlled
' Author:	W. Stephen Woodward

' Setup Parallel Port Addresses
' Pick a parallel port base address from the three possibilities
PP% = &H37A: 						' LPT1
IF INP(PP%) = 255 THEN PP% = &H3BE: 	' LPT2
IF INP(PP%) = 255 THEN PP% = &H27A: 	' LPT3
IF INP(PP%) = 255 
THEN PRINT "***Port NOT Found***"; CHR$(7): STOP

PP% = PP% - 2: ' Compute I/O Address of Output Byte.
' 	< 7    6    5    4     3    2    1    0 >
' 	.PP. = <eclk -1^ +256^ zero   *    *    *    * >
' 	where...
' 		eclk = DAC clk enable
' 		-1^ = toggle to set DAC = DAC - 1
' 		+256^ = toggle to set DAC = DAC + 256
' 		zero = reset DAC to all 0s

' reset DAC and enable clock 
OUT PP%, &H70: OUT PP%, &H60: OUT PP%, &HE0: CR% = 0
   
Calloop:
INPUT "Ampere setting=", I

' Shut off clock and set "^-1" and "^+256" bits 
CR% = (CR% AND 7) OR &H60: 
' then reset DAC and disable clock 
OUT PP%, CR% OR &H10: 
' Divide I up into 8-bit chunks 
MSBY% = I \ 256: LSBY% = I AND 255: 
IF LSBY% 
THEN MSBY% = MSBY% + 1: LSBY% = 256 - LSBY%
IF MSBY% <= LSBY% 
THEN MNBY% = MSBY% ELSE MNBY% = LSBY%
IF MNBY% 
THEN FOR I% = 1 TO MNBY%: CR% = CR% XOR &H60: OUT PP%, CR%: NEXT
IF MSBY% > LSBY% 
THEN FOR I% = 1 TO (MSBY% - LSBY%): CR% = CR% XOR
&H20: OUT PP%, CR%: NEXT
IF LSBY% > MSBY% 
THEN FOR I% = 1 TO (LSBY% - MSBY%): CR% = CR% XOR
&H40: OUT PP%, CR%: NEXT
' Set up to enable DAC clock 
CR% = CR% OR &H80: OUT PP%, CR%
GOTO Calloop