[Coco] Max baud rate for 68681 in MM/1?

[Joel Ewy]

On 01/31/2016 08:44 PM, Kip Koon wrote:
> Hi Joel,
> This is a link for the MC68681 datasheet.
> < http://pdf1.alldatasheet.com/datasheet-pdf/view/4164/MOTOROLA/MC68681.html>
> The maximum speed is 1Mbps.  That should have been a lower case 'b'.

That's kinda what I was thinking.  The question remains as to whether 
the MM/1 can run the 68681 at a higher baud rate than 34,800, and if so, 
is it likely to lose characters.  Part of why I'm asking the question is 
that I'm wondering about the feasibility of doing Drivewire over the 
68681 serial ports.  On the CoCo, 115Kbps is achieved through great 
trickery and masking interrupts for however long it's necessary.  This 
seems to work acceptably well in NitrOS-9.  The ordinary floppy driver 
halted the CPU for a while, waiting for a sector.  The major side-effect 
of this was that the software clock would lose time, hence the 
desirability of no-halt FDCs, like Disto's.  Drivewire largely makes up 
for this problem by giving the CoCo access to the DW server's clock.  
The MM/1 has a DS1287 on the I/O board (with the 68681) which probably 
doesn't have a very good battery anymore after 20 years.  I don't know 
how often the clock module reads from the RTC -- is it only at boot time?

My other thought is that there are some fairly inexpensive 
serial<->ethernet adapters out there with hardware TCP/IP. But it would 
sure be nice to have just a little more speed than 34,800bps.

JCE

> Kip Koon
> computerdoc at sc.rr.com
> http://www.cocopedia.com/wiki/index.php/Kip_Koon
>
>
>> -----Original Message-----
>> From: Coco [mailto:coco-bounces at maltedmedia.com] On Behalf Of Joel Ewy
>> Sent: Sunday, January 31, 2016 4:34 PM
>> To: coco at maltedmedia.com
>> Subject: [Coco] Max baud rate for 68681 in MM/1?
>>
>> I read ambiguous information about the 68681 on the MM/1's I/O board.
>> Does anybody have a definitive word?  Page 2-5 of the MM/1 technical manual claims that it can be run at "1 megabytes per second"
>> (seriously 8M bits/sec?), but the table on page 9-2 and the text on 9-2 state that the maximum baud rate is 34,800.  Is this a pragmatic
>> maximum based on the CPU's ability to service the DUART's on-chip buffers without interrupt-masking trickery, is it the real hard
>> maximum for the 68681, or is it a hard maximum imposed by the MM/1's hardware?  Anybody have any insight?
>>
>> JCE
>>
>>
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