80x86 assembly language drivers – Sensoray 417 User Manual

Page 13

Instruction Manual

80x86 Assembly Language Drivers

;***********************************************************

; Handshake a command byte into the 417 command register.

; Entry:DX points to 417 base port address.

;

AL contains command byte to send to 417.

;***********************************************************

;INITIALIZE DRIVER

XMIT:

PUSH AX

;

Save command byte to be sent to 417

INC DX

;

Set address pointer to status port

;WAIT FOR “COMMAND REGISTER EMPTY”

XLOOP: IN AL,DX

;

Read status port

TEST AL,80H

;

and test CRMT status flag

JE XLOOP

;

Loop until command register is empty

;SEND COMMAND BYTE TO 417 BOARD

DEC DX

;

Set address pointer to command register

POP AX

;

Restore command byte

OUT DX,AL

;

and write it into command register

RET

;EXIT DRIVER

;***********************************************************

; Handshake a byte from the 417 data register.

; Entry:DX points to 417 base port address.

; Exit:AL contains data byte read from 417.

;***********************************************************

;INITIALIZE DRIVER

RCV:

INC DX

;

Set address pointer to status port

;WAIT FOR “DATA AVAILABLE”

RLOOP: IN AL,DX

;

Read 417 status port

TEST AL,40H

;

and test DAV status flag

JE RLOOP

;

Loop until data register is full

;READ DATA BYTE FROM 417 BOARD

DEC DX

;

Set address pointer to 417 data register

IN AL,DX

;

Read byte from data register

RET

;EXIT DRIVER