Other Read/Write Memory Usage - IBM 5170 Technical Reference

Other Read/Write Memory Usage
The IBM BIOS routines use 256 bytes of memory from absolute
hex 400 to hex 4FF. Locations hex 400 to 407 contain the base
addresses of any RS-232C adapters attached to the system.
Locations hex 408 to 40F contain the base addresses of the
printer adapter.
Memory locations hex 300 to hex 3FF are used as a stack area
during the power-on initialization and bootstrap, when control is
passed to it from power-on.
If
the user desires the stack to be in a
different area, that area must be set by the application.
The following figure shows the reserved memory locations.
Address Mode Function
400-4A1 ROM BIOS See BIOS listing
4A2-4EF Reserved
4FO-4FF Reserved as intra-application communication
area for any application
500-5FF
Reserved for DOS and BASIC
500 DOS Print screen status flag store
O=Print screen not active or successful print
screen operation
1 =Print screen in progress
255=Error encountered during print screen
operation
504 DOS Single drive mode status byte
510-511
BASIC
BASIC's segment address store
512-515 BASIC
Clock interrupt vector segment: offset store
516-519 BASIC Break key interrupt vector segment: offset
store
51 A-51 0 BASIC Disk error interrupt vector segment: offset
store
Reserved Memory Locations
If you do a DEF SEG (default workspace segment):
System BIOS 5-9