[Coco] WiFi modem.

[Dave Philipsen]

I think an FPGA implementation of a 6551 would be a fairly easy thing and would not require a huge FPGA. I have a few projects where the synthesis of a nice 6850-compatible UART with a 16 byte receive buffer requires less than 350 LEs including the baud rate generator.  I have used it with data rates up to 1Mbps and it works great. You could even design a UART that could switch between being a 6850 and a 6551 with the flip of a switch. Other options could perhaps be added that would allow larger receive/transmit buffers, non-standard bit rates, etc, etc.

Dave

> On Jan 20, 2018, at 3:21 PM, Gene Heskett <gheskett at shentel.net> wrote:
> 
>> On Saturday 20 January 2018 15:40:30 RETRO Innovations wrote:
>> 
>>> On 1/20/2018 2:35 PM, Gene Heskett wrote:
>>> From the tone of the last message in that thread, it agrees with
>>> mine. Sounds like the NXP SC28L92 might be a far better deal. But
>>> again I've no clue how much support glue other than cs decoding it
>>> might need. If the crosslink is followed, there are pdf's available
>>> there for these chips. QFP44. 10mm sq. looks like a good package
>>> choice. Theres also some sync logic glue samples in one of those
>>> messages.
>> 
>> The main problem is that the 28L92 is not register compatible, so
>> you'd be leaving all existing SW out of luck.  As a general rule, I'm
>> not a big fan of breaking compatibility.
>> 
> All this time I've been aware of that, but then I've always assumed a new 
> driver would present a compatible interface to the user, at least under 
> os9. I am obviously not a fan of rsbasic, which IIRC runs on basic, 
> quite likely with its own serial port code, so that has colored my 
> thinking. A new driver for os9/nitros9 is a relatively minor problem, 
> but that won't make ultimaterm run.
> 
> So you are correct in that you'll have to make an fpga interface that 
> fixes the bug, and is invisible to the likes of ultimaterm. But my 
> experience with fpga's is limited to programming them on the interface 
> cards used between the computer, and the motors that run my machinery, 
> using ready prepared files that I've never had in an editor. In my case 
> I have several choices of interface protocols, using 42 megabaud writes 
> and 25 megabaud reads, 32 bit packets, over an SPI buss fabricated from 
> the gpio pins on the pi's and their ilk. So I can use the same card with 
> an EPP parport interface, (but somewhat slower since even the EPP is 
> limited to about 5 mhz or as an SPI on the same 26 pin header.  So I can 
> program the fpga, but I haven't a clue how to write the program thats 
> written.  So you are several legs up on me.  But I'll sure buy the card 
> if you make it.
> 
>>> I've no clue if NXP is making a 6551 clone thats not broken, but the
>>> fifo's in this chip would certainly be an advantage.
>> 
>> I did not find one.
>> 
>> Jim
> 
> 
> Cheers, Gene Heskett
> The above content, added by Maurice E. Heskett, is Copyright 2018 by 
> Maurice E. Heskett.
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