NB Clock

_System Clock_

by Gerald McMullon

The  COP  provides a system clock  after

each  interrupt (50 times  per  second).

The  COP  scans the keyboard  and  looks

after the relays for the cassette  motor

as  well  as  handling the  VF  display.

Page  zero stores 4 bytes,  the  current

status  of the clock in location 52H-55H

(82-85 decimal).

The  clock  can  be  displayed  by   the

following:

FOR i=1TO1000 :

PUT 12 :

?PEEK(82),PEEK(83),PEEK(84),PEEK(85) :

NEXT i

The  most significant byte is  PEEK(85).

The true value can be found by

?PEEK(85) + 256*( PEEK(84)+256*(

PEEK(83) + 256*PEEK(82) ) )

and can be reset by

FOR i=82to85 : POKE i,0 : NEXT i

On  the  unexpanded NewBrain  or  simple

expansion    (disk    controller)    the

following call locations are available:-

CALL 62383 :REM to reset the clock

CALL 62399, ms : REM to obtain the

system clock time

The  value in seconds is  calculated  by

ms/50.

Example:

5 REM Waste 10 seconds

(approximately)

10 CALL 62383

20 CALL 62399,ms :

IF ms < 500 THEN 20

30 END

The  clock  is  very accurate,  and  has

matched  a  quartz  watch, to  within  a

minute for over 24 hours.

To  time  a piece of code, reset at  the

begining  and  read at the  end  of  the

code.

E.g.

CALL 62383

CALL 62399,no :REM time calls

CALL 62383

...     : REM your code

CALL 62399,ms :

?"Took";(ms-no)/50;"secs"

NB  note  the system clock  is  normally

considered  to be the routines at  62383

and 62399.