Date   : Wed, 07 Jan 2015 11:01:57 +0000
From   : etljwk@... (John Kenyon)
Subject: Serial console active at power-on

On 07/01/2015 07:48, Alan Williams wrote:
> More apologies in advance for the lack of
> attribution/mis-attribution/continuity...
>
> Once I built a 6502 SBC with 32K ram and a 27512 ROM.  The ROM was mapped as
> the MOS and three Sideways roms, one was Basic the 
> other two ROMPAC fileing system, from  which the application booted and
> listened on the serial port.
> I had to do a number of hacks to the MOS to deal with missing hardware (the
> keyboard for a start) and the relocation of the ADC chip and various other
> things.
>
> In the mos there is a table of default values for the *FX settings, so my
> approach was to edit that to give different default values for *FX2 and
> *FX3.  
>
> I have found my notes from 1987.  this may need some corroboration but it
> looks like the rom locations in question may be as follows.
> OSBYTE  RAM  ROM
> 177 &B1 241    D981 is 0 make 1 input source
> 181 &B5 245   D985 is 1 possibly make 0
> 236 &EC 27C   D9BC is 0 possibly make 1 (*FX3)
> 245 &F5 285   D9C5 is 1 possibly make 0 (default printer) 
>
>  I also found a scrap of print out showing a mod I made to the keyboard
> scanner but it's not disassembled from the right address but it goes like
> this.
>
> LDY #&03
> STY &FE40
> LDY #&7F
> STY &FE43
> STX &FE4F
> LDX &FE4F  - Replace with LDX#0:NOP
> RTS
>
> If you are up for blowing a hacked mos chip to achieve a serial console the
> above may help.  You would probably also need to find and fix the default
> baud rate.  Mine was different hardware and was fixed by links.
>
> Alan
>
And while you are at it replace the byte &04 at location &C592 with &00

That will stop VDU 14 from ever setting the page mode bit...

/John