Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!watmath!clyde!cbatt!cbosgd!ucbvax!case.CSNET!bammi
From: bammi@case.CSNET ("Jwahar R. Bammi")
Newsgroups: net.micro.atari16
Subject: Re:  MicroMumps for the ST?      )
Message-ID: <8609290839.AA02705@ucbvax.Berkeley.EDU>
Date: Sun, 28-Sep-86 16:04:36 EDT
Article-I.D.: ucbvax.8609290839.AA02705
Posted: Sun Sep 28 16:04:36 1986
Date-Received: Tue, 30-Sep-86 20:23:18 EDT
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The ARPA Internet
Lines: 40

> As I can think of, there are 3 possibilities:
>
>   (a) replacing the mouse by a tablet (this demands dedicated hardware).
>   (b) connecting a digitizer to the DMA interface (dedicated hardware).
>   (c) connecting a digitizer to an RS-232 interface (general solution).
>
> Although we prefer solution (c), we want the workstation to be connected to
> the VAX all the time: so we would need a second RS-232 interface for the
> ST in that case.
>
>III -Sampling-
>
> Another problem we have is the tablet sampling frequency. This frequency
> should be adjustable from 100 Hz (min.) to 200 Hz or up. Also, the tablet
> should *not* have any intelligence since we want to make a time record of
> the displacements of the pen tip.

	After a couple of moments of thought, i would say why not use the
printer port. Think of the printer port as a parallel Input port with one
interrupt input - the strobe. I would put the serial output of the tablet,
through a Usart, to the parallel input port. The data ready strobe of the
usart would drive the interrupt (strobe) input. The power for the usart can
be tapped off the joystick port.
	Then all that is left to do is to write an interrupt routine to
handle the strobes. There is interrupt reserved for centronics strobe,
that is routed through the MFP and the 68000 see it at IPL6. So your
sampling frequency is only limited by how fast you can process the
interrupt. By putting the usart, you have effectively a 8 bit buffer,
so the sampling rate requirement should go down quite a bit, as now
you are going to sample 8 bits at a time. This should work pretty good with
tablets like the Summargraphics, which i seem to recall, send out data
as 2 4 bit packets in any case (at least that is true in one of the
modes), which the usart will latch and pass on.
	I know its easier said than done, but its another idea off the
top of my head. Hope it helps some.

usenet: .....!decvax!cwruecmp!bammi		jwahar r. bammi
csnet:       bammi@case
arpa:        bammi%case@csnet-relay
compuServe:  71515,155