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Re: Zilog 85c30 RS-422 on Apple IIGS

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On Sunday, October 25, 2015 at 12:07:16 PM UTC-7, D Finnigan wrote:
> John Brooks wrote:
> > Has anyone played with programming the GS SCC for high-speed communication
> > with a PC/Mac over RS-422?
> 
> Have you seen this yet?
> http://macgui.com/downloads/?file_id=11347&keywords=8530
> 
> It's Merlin source to acces the serial port directly (for speed).
> 
> -- 
> ]DF$
> The Marina IP stack for Apple II--
> http://marina.a2hq.com/

Thanks David.

While that code is a good reference for using the GS SCC, it's pretty much designed for 300-57.6k baud speeds using the SCC baud rate generator & async communications via interrupts.

I'm looking more at 230k baud+ synchronous SCC communications.

BTW, if this code is in active use in current GS programs, there are a few things to note:

1) In emulation mode, the IRQ handler doesn't save the Data Bank (B) register and assumes B=0. B can be changed in emu mode and if it is, then the IRQ handler may not only fail to access the SCC registers at $00/$C03x as expected, it will also save it's internal state to the B bank instead of bank 0, corrupting data in that bank.

2) In many cases the IRQ handler is saving more register data than necessary, using more internal state vars than necessary, and using non-optimal addressing modes. Code size, CPU time, IRQ latency, and stack use could be improved somewhat by optimizing the IRQ handler.

HTH,
-JB
@JBrooksBSI

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Zilog 85c30 RS-422 on Apple IIGS John Brooks <jbrooks@blueshiftinc.com> - 2015-10-19 17:59 -0700
  Re: Zilog 85c30 RS-422 on Apple IIGS David Schmidt <schmidtd@my-deja.com> - 2015-10-20 00:09 -0400
    Re: Zilog 85c30 RS-422 on Apple IIGS John Brooks <jbrooks@blueshiftinc.com> - 2015-10-19 21:59 -0700
      Re: Zilog 85c30 RS-422 on Apple IIGS David Schmidt <schmidtd@my-deja.com> - 2015-10-20 01:34 -0400
        Re: Zilog 85c30 RS-422 on Apple IIGS John Brooks <jbrooks@blueshiftinc.com> - 2015-10-19 23:11 -0700
          Re: Zilog 85c30 RS-422 on Apple IIGS David Schmidt <schmidtd@my-deja.com> - 2015-10-20 12:25 -0400
            Re: Zilog 85c30 RS-422 on Apple IIGS John Brooks <jbrooks@blueshiftinc.com> - 2015-10-21 14:58 -0700
              Re: Zilog 85c30 RS-422 on Apple IIGS dempson@actrix.gen.nz (David Empson) - 2015-10-22 13:05 +1300
                Re: Zilog 85c30 RS-422 on Apple IIGS John Brooks <jbrooks@blueshiftinc.com> - 2015-10-21 20:32 -0700
                Re: Zilog 85c30 RS-422 on Apple IIGS dempson@actrix.gen.nz (David Empson) - 2015-10-22 20:08 +1300
                Re: Zilog 85c30 RS-422 on Apple IIGS John Brooks <jbrooks@blueshiftinc.com> - 2015-10-25 18:09 -0700
                Re: Zilog 85c30 RS-422 on Apple IIGS dempson@actrix.gen.nz (David Empson) - 2015-10-26 15:25 +1300
                Re: Zilog 85c30 RS-422 on Apple IIGS John Brooks <jbrooks@blueshiftinc.com> - 2015-10-25 20:12 -0700
  Re: Zilog 85c30 RS-422 on Apple IIGS D Finnigan <dog_cow@macgui.com> - 2015-10-25 19:05 +0000
    Re: Zilog 85c30 RS-422 on Apple IIGS John Brooks <jbrooks@blueshiftinc.com> - 2015-10-25 20:33 -0700
      Re: Zilog 85c30 RS-422 on Apple IIGS D Finnigan <dog_cow@macgui.com> - 2015-10-26 15:25 +0000

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