The BBC and Master Computer Public Domain Library

80E7 Startup Initialisations

Submitted by Steve Fewell

Description:

If the Random Number seed value (&0D-&11) is zero then default the seed value to &0000575241, where:
byte &0D contains #&41, byte &0E contains #&52, byte &0F contains #&57, byte &10 contains 0
and byte &11 contains 0.
Otherwise, leave the Random Number seed at its current value.

Call OSBYTE &84 (Read top of user RAM address) and set HIMEM (&06-&07) to the address returned.
Call OSBYTE &83 (Read operating system high water mark (OSHWM)) and set PAGE (&18) to the MSB of the address returned.

Set the error pointer [addresses &FD-&FE] to point to the Copyright message of the BASIC ROM (which is address &8013).
This sets the last Error Message description to the Copyright message (as shown by typing REPORT after the BASIC ROM
has initialised).
Note: This overrides the MOS default of setting the error pointer to the Version Number of the Language ROM.

Zero byte &1F (LISTO Flag).
Initialise the @% variable:
-> Zero &0402 (@% field 2 - number format = 'general')
-> Zero &0403 (@% field 3 - STR$ number format = 'do not use @% for STR$')
-> Set @% field 0 (Field width) to #&0A (10 characters wide)
-> Set @% field 1 (Number of Decimals to display) to #&09 (Show 9 digits after the decimal point)

Set the BRK vector (&0202-&0203) to address &B2B2 this is the routine that BASIC will run when an error is
generated.
Clear the 6502 Interrupt flag (so that operating system interrupts are now allowed).
jump to &8FF2 for further initialisation.


Changes from BASIC IV: Set the error pointer [addresses &FD-&FE] to point to the Copyright message of the BASIC ROM (which is address &8013).
This didn't need to be done in BASIC IV, as the BASIC 4 ROM doesn't have a Version number (so the MOS will set &FD-&FE
to the copyright message automatically.

Disassembly for the Startup Initialisations routine