On Wed, Jun 23, 1999 at 07:15:04PM +0200, Tomasz Motylewski wrote:
> On Wed, 23 Jun 1999, Peter Wurmsdobler wrote:
>
> > In fact I output 0x0 on ioport 0x2C0 (high byte) and 0x00
> > on 0x2C1 (low byte of 12 bit DAC) which should correspond
> > to -5 Volts. However, I measure 4.37 Volts which tells me
> > that the board registers are set to 0xf and 0x00,
> > respectively. What is different for a 486 in outb() ????
> >
> > /* this corresponds to -5 Volts on the board */
> > outb( 0x00, 0x2c0 ); /* high byte of DAC0 */
> > outb( 0x00, 0x2c1 ); /* low byte of DAC0 */
>
> The only idey I have is different delay. Try to add "udelay(10) between both
> outb, or use outb_p(). It may seem strange, but 486 might be faster in ISA
> output than P133. Just try to play with delays on both computers.
>
Try outputting the low byte first, then the high byte. Many boards
update the DAC only when you write the high byte. This is reasonable,
since you don't want the board to glitch while BASIC is parsing the
next line. (Don't laugh! Just because were enlightened and can do
back-to-back I/O cycles doesn't mean everyone is.
dave...
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