I/O Requests - System Calls - ZiLOG Z80-RIO Operating System User's Manual

Section 3.3) or it may occur as a result of the DEFINE
command (see section 5.14).
As a part of system initialization units 1, 2, and 3
are defined as the console input, console output, and
volume output devices, respectively, and are given the
mnemonics CONIN, CONOUT, and SYSLST. Although these
units are available for redefinition by the user, RIO
assumes that these units represent the equivalent devices.
3.2
I/O REQUESTS - SYSTEM CALLS
I/O requests are accomplished by making
a
subroutine call
to the RIO entry point SYSTEM (see Appendix C). The IY
register must hold the address of a request vector, of the
following format:
IY -)
Byte
o
1
2-3
4-5
6-7
8-9
A
B-C
Logical Unit Number
Contents
logical unit number
request code
data transfer address
data length
completion address
error return address
completion code
supplemental parameter
information
The logical unit number is an integer in the range 1 to
MAXLUN (20 in the standard system). units 1, 2 and 3
are predefined by RIO to be console input, console output,
and volume output.
Request Code
Identifies the operation requested.
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