How to get comm port addresses from BIOS in QB45

Question

I have been using the following code to get comm port addresses from BIOS in QB45:

PRINT "Hex addresses for ports 0 to 3 from BIOS."
DEF SEG = 0
FOR x = 0 TO 3
    z = &H400 + x * 2
    p = PEEK(z)
    q = PEEK(z + 1)
    a = q * &H100 + p
    PRINT " COM" + STR$(x); ": " + HEX$(a)
NEXT
DEF SEG

However when I increase FOR x = 0 to 3 into FOR x = 0 to 7 it returns x378 for 4 (which is lpt1) and 5, 6, and 7, return 0 and I need a way to read comm ports 4, 5, 6, and 7.

I know controlpanel->devicemanager->ports can read them from resources, but I want my basic QB45 program to read them. Any help? Thanks.