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 Mave been described in the earlier magazine issues. All
that now remains is to tidy Up a faw remaining details and to
print the promised hex dump of the monitor extension itsel#.
SYS-EX is written in relocatable code and will operate
correctly at any memory location above 10@eH. However, the
Nasco memory map allocates locations B0eH to B7FFH as the
recommended ‘memory locations for extensions to monitor
facilities. SYS-EX may Conveniently occupy the first half
(B000H to BFFFH) of this available space and at the same tine
provide facilities for the easy use of further extensions from
Should SYS-EX be located at B00CH, two useful and important
facilities are available.
1. The hardware reset jump may be set to cold start SYS-Ex
automatically at switch on and on pressing the RESET
2. NAS-SYS 3 provides the “Y” command which jumps to address
BOGOH. 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
initialieed. 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. [f SYS-EX resides between 1000H
and I2FFH, it may be cold startey by the NAS-SYS command?
If, and only if, SYS-EX resides between 000H and BSFFH, it can
allo be cord started at BE00H.
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
This is an OCR’d
version of the scanned page and likely contains recognition errors.