There is a multikey command but I am not sure if that would work with tinyptc which you are using, there are otehr ways of detecting key presses though.
Here's one way;
'KEYBOARD INPUT
'
'WRITTEN FOR HOTSHOT BY SHOCKWAVE
'
'DETECT THE ARROWS AND SPACE.
'
'-------------------------------------------------------------------------------
' LIBS:
#INCLUDE "TINYPTC_EXT.BI"
#INCLUDE "WINDOWS.BI"
'-------------------------------------------------------------------------------
' KEYBOARD SUBS+ VARS;
'-------------------------------------------------------------------------------
DIM SHARED AS STRING LEFT_KEY
DIM SHARED AS STRING RIGHT_KEY
DIM SHARED AS STRING UP_KEY
DIM SHARED AS STRING DOWN_KEY
DIM SHARED AS STRING SPACE_KEY
DECLARE SUB READ_KEYS()
DECLARE SUB SHOW_INPUT()
'-------------------------------------------------------------------------------
' SCREEN SETUP;
'-------------------------------------------------------------------------------
CONST XRES = 640
CONST YRES = 480
DIM SHARED AS UINTEGER BUFFER ( XRES * YRES )
PTC_ALLOWCLOSE(0)
PTC_SETDIALOG(1,"WWW.RETRO-REMAKES.NET"+CHR$(13)+"FULL SCREEN?",0,1)
IF (PTC_OPEN("Remake code by Shockwave",XRES,YRES)=0) THEN
END-1
END IF
WHILE(GETASYNCKEYSTATE(VK_ESCAPE)<> -32767)
READ_KEYS()
SHOW_INPUT()
PTC_UPDATE@BUFFER(0)
SLEEP 5
ERASE BUFFER
WEND
EXITPROCESS(0)
END
SUB READ_KEYS()
'---------------------------------------------------------------------------
'CHECK LEFT
'---------------------------------------------------------------------------
IF GETASYNCKEYSTATE(VK_LEFT)= -32767 THEN
LEFT_KEY="TRUE"
ELSE
LEFT_KEY="FALSE"
END IF
'---------------------------------------------------------------------------
'CHECK RIGHT
'---------------------------------------------------------------------------
IF GETASYNCKEYSTATE(VK_RIGHT)= -32767 THEN
RIGHT_KEY="TRUE"
ELSE
RIGHT_KEY="FALSE"
END IF
'---------------------------------------------------------------------------
'CHECK UP
'---------------------------------------------------------------------------
IF GETASYNCKEYSTATE(VK_UP)= -32767 THEN
UP_KEY="TRUE"
ELSE
UP_KEY="FALSE"
END IF
'---------------------------------------------------------------------------
'CHECK DOWN
'---------------------------------------------------------------------------
IF GETASYNCKEYSTATE(VK_DOWN)= -32767 THEN
DOWN_KEY="TRUE"
ELSE
DOWN_KEY="FALSE"
END IF
'---------------------------------------------------------------------------
'CHECK SPACE
'---------------------------------------------------------------------------
IF GETASYNCKEYSTATE(VK_SPACE)= -32767 THEN
SPACE_KEY="TRUE"
ELSE
SPACE_KEY="FALSE"
END IF
END SUB
SUB SHOW_INPUT()
IF SPACE_KEY="TRUE" THEN
BUFFER(XRES SHR 1 +((YRES SHR 1 ) * XRES )) = &HFFFFFF
END IF
IF LEFT_KEY="TRUE" THEN
BUFFER((XRES SHR 1) +((YRES SHR 1 ) * XRES )-10) = &HFFFFFF
END IF
IF RIGHT_KEY="TRUE" THEN
BUFFER((XRES SHR 1) +((YRES SHR 1 ) * XRES )+10) = &HFFFFFF
END IF
IF UP_KEY="TRUE" THEN
BUFFER((XRES SHR 1) +(((YRES SHR 1 )-10) * XRES )) = &HFFFFFF
END IF
IF DOWN_KEY="TRUE" THEN
BUFFER((XRES SHR 1) +(((YRES SHR 1 )+10) * XRES )) = &HFFFFFF
END IF
END SUB