rdos/README.md
2019-10-08 10:24:36 +00:00

26 lines
735 B
Markdown

## Memory Layout
On a 8080, there are no segments, the addresses are as displayed.
On on the 8086, a single segment with a value of 0x0100 is assumed.
This implies that the first 4k of memory are not used.
The BDOS may be recompiled for starting at a lower address, in this case,
the minimum memory requirement may be less than 64k.
|Start|Size|Function|
|--|--|--|
|0xF000|4k|BDOS and hw drivers|
||var|BDOS data|
|SP|var|Stack, growing down|
|||Free memory|
|0x0100|up to stack|Transient Program Area|
|0x0080|128 bytes|Command line and disk buffer|
|0x0000|128 bytes|System data area|
## Application program interface
It is using the `call 5` convention with CP/M compatible syscall numbers.
File I/O is done via FCB blocks.