[Coco] DriveWire for TC-9/SWTPC/M68MM17

[Steve]

As Aaron already pointed out, the use of the Bit-banger on the CoCo is 
far from the best solution for transferring data from one computer to 
another.  (Be it drivewire or not.)  The use of a UART, USB or Bluetooth 
hardware solution is preferred over the CPU doing all that work.

The main reason drivewire uses Bit-banging is cost and convenience.  Not 
all CoCo setups have the Deluxe RS-232 pak on them.  Also, a good 
programmer (like Aaron) can fine tune the Big-Banging code to transfer 
faster than the Deluxe RS-232 pak.

There are a number USB and Bluetooth modules that will easily interface 
to these "old time" computers.  Their main advantage besides transfer 
speed is their large FIFO buffers that keeps buffer overrun errors to a 
minimum.  I used a number of hard wired and wireless modules in custom 
projects for the Haunt industry with great success.

Steve


On 12/29/2013 2:47 PM, Joel Ewy wrote:
> Just to confirm my understanding:  The CoCo's Bitbanger uses pins from 
> PIA IC4.  DriveWire for the Dragon uses the same client driver with 
> the addition of a little extra hardware to invert and possibly 
> level-translate the same pins from its 6821 parallel port. Correct?  
> So with a similar adapter one should be able to use one of the TC-9 
> Tomcat's PIAs for DriveWire, and the same should be true of a 6821 
> board on an SWTPC, GIMIX, Motorola Micromodule 17, S-100 6809, or SBC, 
> assuming you are using the driver appropriate to your CPU type and 
> clock speed, and you have a descriptor pointing at the right address.
>
> Actually, as I think about it, the clock speed might be a problem. The 
> DW code is very, very tight and relies on instruction timings that are 
> only going to be valid for the exact clock speed of the CoCo.  So if 
> you have an SWTPC running at 2 MHz it won't be able to run an 
> unmodified DriveWire client written to work at 1.78MHz, will it?  
> Since the TC-9 uses the GIME it is probably running at CoCo 3 speed, 
> though I think I remember FHL claiming some kind of speed-up.  How 
> hard would it be to modify the DW client code to run at 2 MHz or 1 
> MHz?  Or would it be worth it to replace the crystals and drop 10-20% 
> of the CPU clock to get DriveWire?  Hmm.
>
> JCE
>