turbo-pascal-assembly

0460 Write Function

This is Turbo Pascal’s Write(File) function. It takes one parameter:

File: Pointer to the File Record. The bytes that will be written to File are contained within it’s TexBuf. This is usually used when writes are made to the standard Output file.

SYS0460: MOV BX,SP

Use BX to address items on the stack. Upon entry into this subroutine, the stack looks as follows:

Index	Contents
BX	Return Address (OFFSET)
BX+02	Return Address (SEGMENT)
BX+04	Pointer to File/Text Record Data (OFFSET)
BX+06	Pointer to File/Text Record Data (SEGMENT)

SYS0462: PUSH DS

Save DS.

SYS0463: SS:
SYS0464: LES DI,[BX+04]

Loads the pointer to the File into ES:DI.

SYS0467: ES:
SYS0468: LDS DX,[DI:BufPtr]

Loads the pointer to buffer (BufPtr) in File into DS:DX.

SYS046B: XOR CX,CX
SYS046D: ES:
SYS046E: XCHG CX,[DI:BufPos]

Get number of bytes to write from the File’s BufPos.

SYS0471: ES:
SYS0472: MOV BX,[DI:Handle]

Get this File’s Handle.

SYS0474: MOV AH,40
SYS0476: INT 21

Write CX bytes to File/Device using DOS Write to a File or Device INT 21h AH = 40h with parameters:

SYS0478: JB 047C

On error, return with error code in AX.

SYS047A: XOR AX,AX

AX = 0 (No errors).

SYS047C: POP DS

Restore DS.

SYS047D: RETF 0004

Return to caller with error code in AX, later to be stored in InOutRes. Pop-off FAR PTR parameter from the stack (4 bytes).