Calling ROM BASIC from DOS 2.1?

[lyonadmiral]

I know you use the debugger, but I'm not familiar with the debug syntax. What is the command to call ROM BASIC? I thought int 18th, but I'm obviously wrong.

Thanks,
Dan

 

[vwestlife]

That is correct, but you can't enter an INT directly into DEBUG's command prompt. You have to write it as a small assembly language routine and then run it. From memory, here's how the DEBUG session would go:

a 100 (to start the assembler)
int 18
<CR> (hit Enter to return to DEBUG prompt)
g=100 (to run the assembler code you just entered)

Doing this on a PC without BASIC in ROM would cause a boot failure error, the same as you get when you attempt to boot from a hard drive which has been partitioned but not formatted yet.

 

[Chuck(G)]

Depending on the (IBM) BIOS, setting ES=0000 may also be required before the INT 18H.

 

[per]

Depending on the (IBM) BIOS, setting ES=0000 may also be required before the INT 18H.

In the XT boot routine, DS is also set to 0000 in addition to ES before Int 18h is being called.

 

[Mike Chambers]

as mentioned, interrupt 18h will kick off ROM BASIC. it's entry point is actually F600:0000 and it takes up the 32 KB immediately below the 8 KB of BIOS ROM code.