inkey.scr
n inkey.com
e 0100 b4 08 cd 21 b4 4c cd 21
rcx
0008
w
q

menu1.bat
@echo off
:menu
cls 
echo a: dir
echo 0: bye
inkey.com
if errorlevel 65 if not errorlevel 66 goto dodirw
if errorlevel 97 if not errorlevel 98 goto dodirw
if errorlevel 48 if not errorlevel 49 goto end
goto menu
:dodirw
dir /w
goto end
:end
echo bye bye

key.scr
n key.com
e 0100 b4 00 cd 16 3c 7a 77 06 3c 60 76 02
e 010c 24 df 3c 00 75 02 88 e0 b4 4c cd 21
rcx
0018
w
q

61 = "a" = 0110 0001
7A = "z" = 0111 1100
41 = "A" = 0100 0001
5A = "A" = 0101 1100
DF = 1101 1111

JA = Jump if Above ถ้าสูงกว่า
JBE = Jump if Below
JNZ = Jump if Not Zero

menu2.bat
@echo off
:menu
cls 
echo a: dir
echo 0: bye
key.com
if errorlevel 65 if not errorlevel 66 goto dodirw
if errorlevel 48 if not errorlevel 49 goto end
goto menu
:dodirw
dir /w
goto end
:end
echo bye bye