PORTIBM PC Portable (uses same BIOS as XT) 0210-0217 - Expansion unit (XTIBM PC XT) 0210 -W latch expansion bus data 0210 R- verify expansion bus data 0211 -W clear wait, test latch 0211 R- High byte data address 0212 R- Low byte data address 0213 -W 0=enable, 1=disable expansion unit 0214 -W latch data (receiver card port) 0214 R- read data (receiver card port) 0215 R- High byte of address, then Low byte (receiver card port)