Tandy 1000 Programmer's Reference Manual page 18

Chawter 1 I
Svstem Calls
CONTROL-C Exit Address
Interrupt 23H
If
the
display
tor in
user types
CONTROL-C
during keyboard input
or
output, control transfers t o the Interrupt 23H vec-
the interrupt table. This address is copied into the
Program Segment Prefix from the Interrupt 23H vector
when the segment is created. You can set this address us-
ing Function Call 25H.
If the CONTROL-C routine saves all registers, it can end
with an IRET instruction (return from interrupt) to con-
tinue program execution. When the interrupt occurs, all
registers are set to the value they had when the original
call to MS-DOS was made. There are no restrictions on
what a CONTROL-C handler can do (including MS-DOS
function calls) as long as the registers are unchanged if
IRET is used.
If Function 09H or OAH (Display String or Buffered Key-
board Input) is interrupted by CONTROL-C, the 3 byte
sequence 03H-0DH-0AH (ETX-CR-LF) is sent to the dis-
play and the function resumes at the beginning of the
next line.
If the program creates a new segment and loads a second
program that changes the CONTROL-C address, termina-
tion of the second program restores the CONTROL-C ad-
dress to the value it had before execution of the second
program.
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