[Coco] Coco 3 Memory Map Questions

[RETRO Innovations]

On 2/7/2016 4:25 PM, L. Curtis Boyle wrote:
> Isn't the 16 bit access to memory more for the GIME, for accessing graphics memory to send to the screen?
I initially discounted that, because GIME has an 8 bit path.  But, I 
think you are correct.

U10 and U11 bridge the CPU data lines to the RAM lines when WE0 and WE1 
are low.  If I assume WE0 goes low on even memory address and WE1 goes 
low on odd, that's what that circuit does.

U12 and U13 do indeed bring in 16 bits.  When CAS goes low, U12 bridges 
the even? data bank to GIME.  When CAS goes high, U13 latches the odd? 
data bank and also bridges the latched data into GIME.

Looking at the schematic, other items that makes me wonder:

  * It looks like to save 1 pin on GIME, Tandy brought out S0,S1,S2
    select lines to a '138 to select 4 different IO spaces (SCS, CTS,
    ROM and the two PIAs).  I wonder if the other 4 select lines are
    decoded to some spot in memory.
  * Has anyone figured out what happens if the "test" line is brought
    low?  I see some discussion about it online, but no results of it
    being exercized.

Jim