Date   : Fri, 24 Feb 2017 22:42:22 +0000
From   : jgh@... (J.G.Harston)
Subject: Emulation

Julian Stenning wrote:
> My question now is what part of the OS picks up that this keyboard
> input has to be written to the VDU?

OSWORD 0 - Read input line. This does, effectively:
LEN=0
REPEAT
   A=OSRDCH
   IF (A in range) THEN MEM[LEN]=A:LEN++:OSWRCH
   IF (A=127) AND LEN>0 THEN LEN--:OSWRCH
UNTIL A=13 OR ESCAPE

To bypass getting the keyboard working you could configure the MOS so it 
starts up with serial as the input stream. You need to set the default 
*FX2 value to 1 'input from serial port', and then implement a simple 
8bit+Ready input port.

The default startup values are stored at the address in &FFB7/8. This 
points to the default page &02 values. So, the first &36 bytes are the 
default vectors, the following bytes are the default values for OSBYTE 
&A6 onwards.

The input stream is stored in *FX177, so, to start up with serial as the 
input stream, set !&FFB8+(177-112) to 1. If you are manipulating just 
the 16K ROM image, offset=rom[0x3FB8]+256*rom[0x3FB9]-0xC000; 
rom[offset+177-112]=1;

-- 
J.G.Harston - jgh@...      - mdfs.net/jgh