Set delay directly from n, not p

As written, if you set p and n, e.g. with `5,120A` to put a PWM value of 120 on pin 5, then issue a `0D`, the delay will actually be set to 5 us. Probably should move handling of 'D' out of the case and up in the loop just before the `if (0==n) {n=p; }` and manage with `if ('D'==cmd) {d = n; n=0; continue;}`

But test that really well if you do it. 