Date   : Mon, 03 Mar 2008 19:45:17 -0000
From   : dl.harper@... (David Harper)
Subject: TUBE chip, accessing 'Parasite' side

Johan Heuseveldt wrote:

> I'm sort of 'designing' a CoProcessor with a 6809 - 2 MHz version (68B09).
>
> I refound the schematics for the internal CoPro 80186, but couldn't find
> anything else. With my own 6502 external 2ndProcessor, I've investigated a
> few things. It appears that the power connections to the TUBE chip are 
> more
> advanced than I first assumed, which makes sense as this chip - besides 
> the
> logical model for the TUBE software protocols - must also handle two
> independant power connections, and some safety precautions are apperently
> necessary!
>
> Further, I was looking at the access of the 3 MHz 6502 to the TUBE chip,
> and found it was different than expected. Investigating this board any
> further will be a project of its own, I suppose, so I tried to look for it
> elsewhere. No luck though.
> The 80186 schematics are also vague (to me) in this respect.

Don't follow the 80186 too exactly. It is somewhat non-standard. (For 
instance, it uses a connection to DRQ to prompt for data transfers. The 
standard is to use NMI, but the 80186 co-pro has to use NMI in a totally 
different way to get over a problem with certain DOS programs.)

> The '004' document for the TUBE doesn't say anything how fast the parasite
> side can/may be accessed. Even an pin description is without pin numbers.
>
> So, does anybody know how fast the parasite side can be accessed by the
> processor?
> I assume that at least for a 2 MHz processor, no slow-down is needed?

The Tube interface is itself designated as 2MHz.

There are specified minimum speeds that the parasite must be able to deliver 
data to the host, or receive data from it. (For speed, the host code reads 
and writes without any checks of whether there is any data in the buffer of 
not. If the parasite is too slow, then data will be lost.) On the other 
hand, it does not matter if the parasite is faster, since it reads and 
writes under interrupt control (or DRQ for the 80186).

If you have the 80186 schematic diagram, you should at least be able to work 
out the pin numberings for the Master's internal Tube from it, as well as 
the numberings on the Tube ULA chip. The pin numberings for the external 
Tube can be read off the schematic diagram of the Master provided at the 
back of Watford Electronics' "Advanced Reference Manual for the BBC Master".

David Harper