| FDEC |
Scroll-screen check, looks to see if the
next character would cause a scroll, checks the page mode
counter (?E6), and executes a scroll or waits for a
keypress.
FE08 - Scroll the screen. Entry at FE0A with Y=40 will
scroll all but the top line of the screen. Y-60 leaves
the top two lines alone, etc.
FE22 - delete all current line.
FE24 - blank Y+1 characters in current line.
FE26 - fill Y+1 characters from current line onward with
the character in the accumulator.
FE35 - Check Next Cursor Position, called by Backspace
and Delete to see if the cursor is at the beginning of a
line or Home position, |
| FE52
to FE65 |
Routine to print a character. This is
indirected by (208), called by the OSWRCH at FFF4.
FE52 - Pass character to VIA printer, and execute.
FE55 - Pass character on screen or execute any
recognisable control codes. X and Y registers preserved. |
| FE66
to FE70 |
A subroutine to synchronise to CRT Field
Flyback, used to write on the screen without generating
noise. Can be used as a timer.
FE66 - wait until the start of the next field flyback,
even if already in flyback.
FE6B - return immediately if already in flyback, else
wait until the next flyback. A, X, Y all preserved. |
| FE71
to FE93 |
The Keyscan Subroutine called by OSRDCH
(see below). Does not examine <CTRL>,
<SHIFT>, <RPT> or <BREAK>. It returns
with the carry flag set if no key was pressed. If a key
was pressed when this routine was called, the carry flag
is cleared and the Y register holds the key pressed as
its ASCII value minus hex 20. |
| FE94
to FECA |
OSRDCH Subroutine. This routine waits
for a key to be pressed and then returns with its ASCII
value in the accumulator. Cursor and some other control
codes are executed BEFORE returning. |
| FECB
to FEFA |
Data and look-up tables for executing
control codes. |
| FEFB
to FF3E |
A subroutine called by OSWRCH to pass
the value of the accumulator to the printer using the
VIA. <CTRL> B and C enable or disable this routine
respectively.
FF10 - waits for handshake signal (see chapter 7). |
| FF3F
to FF99 |
RESET - the machine comes here after
hitting <BREAK> or at switch-on, by picking up the
reset address at FFFC (common to all 6502
microprocessors).
FF3F - initialise page 2 vectors (204 and up)
FF4A - set stack pointer to FF.
FF53 - set all array pointers to FFFF.
FF69 - print message 'ACORN ATOM'.
FF7C - test for RAM at 2900, and set text pointer to
default values if appropriate. |
| FF9A
to FFB1 |
Data used by the RESET routine to
initialise page two vectors. |
