[HECnet] DDCMP sync?

[Mark Curtis]

The Z85C30 is indeed still available - I got one recently - you can get 
them on mouser at various speed ratings (8 and 10s mainly). No doubt 
other places will supply them as well.


M

On 26/01/2021 05:53, Dave McGuire wrote:
> On 1/25/21 8:46 PM, Paul Koning wrote:
>> In playing with DECnet I built a DDCMP implementation which deals 
>> with a byte stream, normally from a UART.  So that works nicely with 
>> async link DDCMP as found in RSX and several other operating 
>> systems.  But the speed is limited.
>>
>> The other option would be synchronous links, which would enable 
>> connections to DMC11 or the like at speeds up to 1 Mb/s.  But 
>> synchronous comm devices that connect to modern computers aren't so 
>> easy to find, though I have seen a few.
>>
>> After playing with Arduino for LK201 keyboard emulation I started to 
>> wonder if one could be made to be a synchronous comm link with a USB 
>> back end, with low level things like byte framing and maybe DDCMP 
>> packet format handling in there, but the protocol state machine in 
>> the host behind the USB interface. For moderate speeds that seems 
>> entirely practical.  For 1 Mb/s, probably not, though perhaps one of 
>> the fast ARM based units with its built-in SPI could be warped into 
>> that.
>>
>> The alternative would be something like a BeagleBone Black (or Green) 
>> such as David Gesswein used as the engine for his MFM hard disk 
>> emulator.  That clearly could do the job without any strain.
>>
>> So I'm wondering: would there be interest in such a thing?  If yes, 
>> should it be a modem-connected one (RS232 signaling, bit clock 
>> supplied externally by a modem or modem-eliminator)?  Or should it be 
>> the "integral modem" short distance type, the ones that used a pair 
>> of coax with 4-pin AMP connectors like this 
>> https://www.digikey.com/en/products/detail/te-connectivity-amp-connectors/206060-1/15588 
>> ?
>
>   You could implement it as a USB interface to a Z8530 or a Z80 SIO, 
> they both do synchronous serial, and most likely implement all of the 
> required functionality.  They're both readily available, and likely 
> will be for a long time.  I think the Z8530 may even still be current, 
> but I've not checked.
>
>   Just a thought.
>
>             -Dave
>