I think you're right about the drive side signals being at TTL levels and not 
'true' RS232, but if you have another look at the T200 schematic (or actually 
measure) I think you'll find that like the other model Ts it does indeed 
conform to the RS232 spec with a swing of -5V to +5V.

I believe the 'special cable' takes care of the necessary translation.


----- Original Message ----- 
From: <biggran...@tds.net>
To: <m...@bitchin100.com>
Sent: Wednesday, August 09, 2017 1:52 PM
Subject: Re: [M100] PDD Firmware Reverse Engineering - Progress

> There should be a little difference in speed, the data to and from the 
> disk in not streamed, it is buffered in RAM in chunks on the drive 
> controller board and then transferred to disk (or back to serial). And 
> everything is done asynchronously.
> I'm sure 19200 was chosen for robustness though, the RS232 interface on 
> the drive controller is not a proper implementation and only provides 0 
> to 5V signaling for "mark" and "space", not the proper -3V to -15V for a 
> "mark" and +3V to +15V for a "space". And looking at the schematic for 
> the T200, it's the same way too.
> Darren
> On 8/9/2017 1:27 PM, John R. Hogerhuis wrote:
>> Interesting! I wonder if it can actually do 76800bps since it's in 
>> their baud rate table.  I've found that's the top speed of the model 
>> 100. I don't think the t200 can reach it though. I think the t200 will 
>> function at 38400 but I don't remember for sure.
>> Not that it matters too much. It's a disk drive so we're limited by 
>> the speed of the drive itself.
>> -- John.

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