Octagon 5266, Справочное руководство

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Built-in BIOS function definitions
This section provides definitions for the following built-in functions: Initialize I/O,
Write I/O, and Read I/O. These functions can only be used with DOS operating
systems. If you use a different operating system, the functionality can still be used
by your application but must be integrated into your software.
Initialize I/O
Function: efh
Subfunction: 00h
Purpose: To set the directions and to program the
initial values of an I/O port.
Calling registers: Ah efh
AL 00h
DI Port A configuration
Initial Data Direction Mask
xxxxxxxx xxxxxxxxB
direction: 1=output, 0=input
BX Port B configuration
Initial Data Direction Mask
xxxxxxxx xxxxxxxxB
direction: 1=output, 0=input 0->input
CX Port C configuration
Initial Data Direction Mask
xxxxxxxx xxxxxxxxB
direction: 1=output, 0=input
DX ffffh
AL Error code
Comments: This function is used to initialize the
I/O before normal use.
Programming example:
/* Inline assembly code for Borland C++ 3.1 */
asm {
mov ax,0ef00h
mov di,00ffh /*port A all outputs,
init data=all 0’s */
mov bx,55ffh /*port B all outputs,
init data=55h*/
mov cx,0000h /*port C all inputs*
mov dx,0ffffh
int 17h
}
Write I/O
Function: efh
Subfunction: 01h
Purpose: To write a value to an I/O port.
Calling registers: AH efh
AL 01h
DI Port A mask and data
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