SYS-EX A 1K extension program for NAS-SYS monitors. Part 5
by David G. Johnson
This is the final part of the series of articles on the 1K
monitor extension to NAS-SYS. All of the major facilities of
SYS-EX have been described in the earlier magazine issues. All
that now remains is to tidy up a few remaining details and to
print the promised hex dump of the monitor extension itself.
SYS-EX is written in relocatable code and will operate
correctly at any memory location above 1000H. However, the
Nascom memory map allocates locations B000H to B7FFH as the
recommended memory locations for extensions to monitor
facilities. SYS-EX may conveniently occupy the first half
(B000H to B3FFH) of this available space and at the same time
provide facilities for the easy use of further extensions from
Should SYS-EX be located at B000H, two useful and important
facilities are available.
The hardware reset jump may be set to cold start SYS-EX
automatically at switch on and on pressing the RESET
NAS-SYS 3 provides the “Y” command which jumps to address
B000H. The “Y” command can be used directly to cold start
Cold starting SYS-EX
A cold start is required if the monitor has not already been
initialised. e.g. at switch on or after a program has made non
standard use of the memory reserved for NAS-SYS workspace.
The execution address for cold starting SYS-EX is 5 bytes on
from the start of SYS-EX. e.g. If SYS-EX resides between 1000H
and 13FFH, it may be cold started by the NAS-SYS command:
If, and only if, SYS-EX resides between 8000H and B3FFH, it can
also be cord started at B000H.
Warm starting SYS-EX
A warm start is used when the initialisation of the NAS-SYS
workspace and the clearing of the screen memory are not