INT 14 - Digiboard DigiCHANNEL PC/X* - SEND BIOS COMMAND
AH = 18h
ES:BX -> 16-byte command string
DX = port number (00h-03h) (04h-43h for XAPCM232.SYS)
Return: AH = status
00h successful
80h timeout
AL = mailbox status
00h no errors
8Xh BIOS error
ES:BX buffer filled in with mailbox string
ZF clear if no errors
ZF set if either status byte contains an error code

See also: 1416

1418 - Digiboard DigiCHANNEL PC/X* - SEND BIOS COMMAND