IBM XT 5160 Technical Reference page 313

LOC OBJECT LINE SOURCE (BIOS FOR THE I BM PERSONAL COMPUTER XT) 11/08/82
5013
5014 ; ----- OETERM I NE ALPHA CHAR POS I T I ON
5015
F80A 8AD4 5016 MOV DL,AH COLUMN VALUE FOR RETURN
F80C 8AFO 5017 MOV DH,AL
ROW VALUE
F80E DOEE 5018 SHR DH,I
01 V IDE BY 4
F8l0DOEE
5019
SHR
DH,I FOR VALUE IN 0-24 RANGE
F812 EB12
5020
JMP SHORT V5 LIGHT _PEN_RETURN_SET
5021
5022 ; - - - - - ALPHA MODE ON LI GHT PEN
5023
F814 5024 V4:
ALPHA PEN
F814 F6364AOO 5025 DIV BYTE PTR CRT_COLS DETERM I NE ROW, COLUMN VALUE
F818 8AFO 5026 MOV DH,AL ROWS TO DH
F8IA 8AD4 5027 MOV DL,AH COLS TO DL
F8IC D2EO 5028 SAL AL,CL
MULT IPLY ROWS •
8
F8IE 8AE8 5029 MOV CH,AL GET RASTER VALUE TO RETURN REG
F820 8ADC 5030 MOV BL,AH COLUMN VALUE
F822 32FF 5031 XOR BH,BH TO BX
F824 D3E3 5032 SAL BX,CL
F826 5033 V5:
LIGHT PEN RETURN SET
F826 B40 I 5034 MOV AH,1
INDICATE EVERTHING SET
F828 5035 V6:
LIGHT PEN RETURN
F828 52 5036 PUSH OX SAVE RETURN VALUE
(IN CASE)
F829 8B 166300 5037 MOV DX,ADDR_6845 GET BASE ADDRESS
F82D 83C207 5038 ADD DX,7 PO I NT TO RESET PARM
F830 EE 5039 OUT DX,AL ADDRESS, NOT DATA,
IS IMPORTANT
F831 5A 5040 POP OX
RECOVER VALUE
F832 5041 V7:
RETURN_NO_RESET
F832 5F
5042 POP 01
F833 5E 5043
POP
SI
F834 IF 5044 POP OS DISCARD SAVED BX, CX, OX
F835 IF 5045 POP OS
F836 IF 5046 POP OS
F837 IF 5047
POP OS
F838 07 5048
POP ES
F839 CF 5049 IRET
5050 READ_LPEN ENDP
5-166
PC-XT System BIOS (11/08/82)