Re: [M100] PDD Firmware Reverse Engineering - Progress

[John R. Hogerhuis]

On Wed, Aug 9, 2017 at 1:49 PM,  wrote:

> Yes, you're right. I just took a quick look at the T200 schematic and saw
> few gates sitting at the RS232 connector, I didn't notice the VEE at the
> bottom (plus the image is very pixelated too).
>
>
Well, also the TPDD cable itself has active electronics in it that do level
shifting.

-- John.

Re: [M100] PDD Firmware Reverse Engineering - Progress

[BiggRanger]

Yes, you're right. I just took a quick look at the T200 schematic and 
saw few gates sitting at the RS232 connector, I didn't notice the VEE at 
the bottom (plus the image is very pixelated too).




On 8/9/2017 4:20 PM, Mike Stein wrote:

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.

m

- 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.

Re: [M100] PDD Firmware Reverse Engineering - Progress

[Mike Stein]

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.

m

- 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.
> 
>

Re: [M100] PDD Firmware Reverse Engineering - Progress

[BiggRanger]

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.

Re: [M100] PDD Firmware Reverse Engineering - Progress

[John R. Hogerhuis]

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.

Re: [M100] PDD Firmware Reverse Engineering - Progress

[Daryl Tester]

Love your work!

I do have a TPPD2 here, but not the time to look at it.  All my hobbies
have fallen by the wayside at the moment. :-/

On Tue, 8 Aug 2017 22:48:04 -0400, biggran...@tds.net wrote:


For those who are interested...
Getting a copy of the PDD1 Software Manual really helped out with the
reverse engineering effort!

I've figured out a few command tables and added a bunch of
documentation to the assembly source.

I've updated the reverse engineering project here:
https://github.com/BiggRanger/Tandy_PDD
PDD.ASM has all the important stuff.


...

--
Regards,
  Daryl Tester
  Handcrafted Computers Pty. Ltd.