DIN sync in x0x boxes (was RE: [sdiy] Help-Blacet midi-din sync chip problems!)

[Colin Fraser]

> -----Original Message-----
> From: owner-synth-diy at dropmix.xs4all.nl 
> [mailto:owner-synth-diy at dropmix.xs4all.nl] On Behalf Of John Blacet
> Sent: 11 February 2002 4:14
> To: synth-diy at dropmix.xs4all.nl
> Subject: Re: DIN sync in x0x boxes (was RE: [sdiy] 
> Help-Blacet midi-din sync chip problems!)
> 
> 
> "Given this fact, I'm surprised the Blacet chips work well at 
> all in the
> 
> recommended configuration. 1ms just shouldn't be long enough."
> 
> ---At least one user of these chips has reported upping the 
> pulse width
> to 2 mS. Note that this is EXTERNAL circuitry and thus is 
> easily changed
> via resistor or cap value.

The fact it's an external pulse stretch does mean it should be very easy
to fix if there are any problems with devices that poll for the clock
signal.
It's quite likely that if you haven't had any users with problems, the
pulse length of the datasheet example might be longer than you think.

Polling is bad practice anyway - if Roland had ORed the sync input into
the interrupt line, they could have used a lower refresh rate for the
LEDs etc, and still been sure of catching every clock pulse at it's
leading edge.
But maybe the 1.8ms polling interval, which should give an average
timing error of about 1ms, is responsible for the 'feel' of the 303
sequencer ;-)

Colin f