Nascom News­let­ter

extension code. Any calls to NAS-SYS or SYS-EX routines from within the extension code will require a number of stack levels to be available.

Suggested routine to extend SYS-EX at offset 0400H

Compatibility with NAS-SYS monitors

Compatibility with both NAS-SYS 1 and NAS-SYS 3 monitors is achieved (with one exception) by calling the NAS-SYS routines in the NAS-SYS recommended manner.

The one exception is that SYS-EX requires access to the absolute address of the NAS-SYS INLS routine, which is different in the two versions of NAS-SYS, This is achieved by locating the instruction in the main monitor loop PARSE (by using a variant of the SYS-EX FCEP1 routine) which follows the NAS-SYS call to INLS in both versions of the monitor. The address of INLS is taken from the two bytes prior ta this common instruction.

User entry point summary