Sharp MZ-800 - Page 142

OUT@
Format OUT@ <port number>, <numeric expression>
Explanation The OUT@ statement converts the decimal number specified in <numeric expres-
sion> (0 to 255) to a binary format and sends it to the output port specified in
<port number>. <port number> may range from 0 to 127 (hexadecimal $00 to
$7F). Port addresses 128 to 255 (hexadecimal $80 to $FF) are reserved for optional
peripheral devices.
Peripheral devices are controlled by data transmitted to I/O ports. Consequently,
specifying an illegal number in <port number> may cause peripheral device mal-
function.
USR
Format USR (<address>[,<input string variable>] [,<output string variable>])
Abbreviated Format
Explanation
U.
The USR function transfers control to a machine language program which starts
at the specified address. As with CALL <address>, control is returned to the state-
ment following the USR function when a return instruction RET or RET cc is en-
countered in the machine language program. <address> must be a decimal or 4-digit
hexadecimal number.
The parameters are loaded into the following registers when the main program trans-
fers control to the machine language program:
DE register: Starting address of <input string variable> in memory.
B register: length of <input string variable>.
IX register: address of the error processing routine, if declared.
The machine program loads processing results into the following registers when it
returns control to the main program:
DE register: starting address of <output string variable> in memory.
B register: length of <output string variable>.
The following steps are necessary when error processing is required in the machine
language program:
1. Declare an error processing routine in the BASIC program using an ON
ERROR GOTO statement.
2. Write a program segment which loads the A register with the error code and causes
program execution to jump to the address specified in the IX register.