[Coco] Dual UART with FIFO Card for the CoCo

[Phill Harvey-Smith]

Gene Heskett wrote:
> On Sunday 13 June 2010, Phill Harvey-Smith wrote:
>> Gene Heskett wrote:
>
> There is an echo in here Phill. ;-)  And as long as we use modern cmos 
> chips, the additional drain on the coco's supply should be minimal, 
> particularly if we replace some of the old hungry TTL stuff that wouldn't be 
> needed as it would just dup what we'll do but we'll do it better.

Indeed, though there is one fly in the ointment I noticed from the CoCo 
rom disassebilies, the Init code on the CoCo 1/2 actually takes 
advantage of the mirrored PIA 1 addresses :(

A02A 8E FF 20       LA02A    LDX     #PIA1    	POINT X TO PIA1
A02D 6F 1D                   CLR     -3,X       CLEAR PIA0 CONTROL 
REGISTER A
A02F 6F 1F                   CLR     -1,X       CLEAR PIA0 CONTROL 
REGISTER B
A031 6F 1C                   CLR     -4,X       SET PIA0 SIDE A TO INPUT
A033 CC FF 34                LDD     #$FF34     *
A036 A7 1E                   STA     -2,X       * SET PIA0 SIDE B TO OUTPUT
A038 E7 1D                   STB     -3,X       * ENABLE PIA0 PERIPHERAL 
REGISTERS, DISABLE PIA0
A03A E7 1F                   STB     -1,X       * MPU INTERRUPTS, SET 
CA2, CA1 TO OUTPUTS
A03C 6F 01                   CLR     1,X        CLEAR CONTROL REGISTER A 
ON PIA1
A03E 6F 03                   CLR     3,X        CLEAR CONTROL REGISTER B 
ON PIA1
A040 4A                      DECA               A REG NOW HAS $FE
A041 A7 84                   STA     ,X         BITS 1-7 ARE OUTPUTS, 
BIT 0 IS INPUT ON PIA1 SIDE A
A043 86 F8                   LDA     #$F8       =
A045 A7 02                   STA     2,X        = BITS 0-2 ARE INPUTS, 
BITS 3-7 ARE OUTPUTS ON B SIDE
A047 E7 01                   STB     1,X        * ENABLE PERIPHERAL 
REGISTERS, DISABLE PIA1 MPU
A049 E7 03                   STB     3,X        * INTERRUPTS AND SET 
CA2, CB2 AS OUTPUTS
A04B 6F 02                   CLR     2,X        SET 6847 MODE TO 
ALPHA-NUMERIC
A04D C6 02                   LDB     #$02       *
A04F E7 84                   STB     ,X         * MAKE RS232 OUTPUT MARKING

By the looks of things both the Dragon 32 and 64 roms don't have the 
same problem, however the 64 has the 6551 ACIA at $FF04-$FF08. I guess 
the Tandy roms could probably be fixed, but that would mean blowing new 
roms to do so.

>  We just need to standardize how its done so that we don't have 250 
> individually unique versions, one for each of us left.  That would be a 
> disaster to the group as a whole.

Indeed :(

> Hint, leave the stuff at $ff40+ alone, because many of us have worked out 
> what works for us already.

That would seem sensible.

Cheers.

Phill.

-- 
Phill Harvey-Smith, Programmer, Hardware hacker, and general eccentric !

"You can twist perceptions, but reality won't budge" -- Rush.