Tandy 1000 Basic Reference Manual

Chapter 10 I BASIC Keywords
USR
Function
USR[ nu m ber] (argument)
Calls a user’s assembly-language subroutine identified with
number and passes argument to that subroutine.
The
number you specify must be the same as the corresponding
DEF
USR statement for that routine. If you omit number, BASIC
assumes zero.
USR lets you call as many as 10 assembly-language subroutines
and then continue execution
of your BASIC program.
Before you can execute
a USR function call, you must define the
subroutine’s address in a DEF SEG and DEF
USR statement.
The DEF SEG defines the address
of the segment containing the
subroutine. The DEF USR statement defines the subroutine
being called and its offset from the beginning
of the segment set
by DEF SEG. See DEF SEG, DEF
USR, and the section “Inter-
facing With Assembly-Language Subroutines” in Chapter
11.
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Tandy 1000 Specifications

General

Processor	Intel 8088
Processor Speed	4.77 MHz
RAM	128 KB (expandable to 640 KB)
Operating System	MS-DOS 2.11
Manufacturer	Tandy Corporation
Release Year	1984
Storage	Single or double 5.25" floppy disk drive (360 KB), optional hard drive
Sound	Tandy 3-voice sound
Ports	Parallel, Serial
Graphics	CGA (Color Graphics Adapter)
Graphics Modes	320x200, 640x200