Hardware device absolute adressess:
DFE00 - DFE06: Unknown PAL device (4 addresses accordin to 1101 rev3 BIOS code)
DFF00 - DFF08: Uart 8274 (2 address lines, 4 addresses)

rev4 MB (new):

seg000:22D0 a33000022551000 db '330000225510--0044 <<-- ppaarrtt nnuummbbeerr'
lower IC: 300250-04 <- part number
upper IC: 300251-04 <- part number

seg000:0406 ; =============== S U B R O U T I N E =======================================
seg000:0406 setupUART       proc near               ; CODE XREF: seg000:loc_FC47E↓p
seg000:0406                 push    ds
seg000:0407                 mov     ax, 0DFF0h
seg000:040A                 mov     ds, ax
seg000:040C                 assume ds:hwUART
seg000:040C                 mov     byte ptr ds:4, 18h
seg000:0411                 mov     byte ptr ds:6, 18h
seg000:0416                 mov     ax, 0DFE1h
seg000:0419                 mov     ds, ax
seg000:041B                 assume ds:hwUnkonown
seg000:041B                 mov     byte ptr ds:0, 0
seg000:0420                 mov     byte ptr ds:2, 0FFh
seg000:0425                 mov     byte ptr ds:4, 0FFh
seg000:042A                 mov     byte ptr ds:6, 0
seg000:042F                 pop     ds
seg000:0430                 assume ds:nothing
seg000:0430                 retn
seg000:0430 setupUART       endp

seg000:3C00 loc_FFC00:                              ; CODE XREF: seg000:3FF0↓J
seg000:3C00                 cli
seg000:3C01                 mov     ax, 0DFE0h
seg000:3C04                 mov     es, ax
seg000:3C06                 assume es:hwUnkonown
seg000:3C06                 mov     al, 0
seg000:3C08                 mov     es:0, al
seg000:3C0C                 mov     es:2, al
seg000:3C10                 mov     es:4, al
seg000:3C14                 jmp     SEG_MAIN:CompassPromStart


            ;j_BiosEntryPoint proc far
            j_BiosEntryPoint:
seg000:3FF0                 jmp     far ptr loc_FFC00
            ;j_BiosEntryPoint endp

;========================================================================================
rev3 MB (OLD):
part_number:    db '330000114432--0044 <<-- ppaarrtt nnuummbbeerr'
lower IC: 300142-04 <- part number
upper IC: 300143-04 <- part number

;setupUART       proc near
setupUART:
                push    ds
                mov     ax, 0DFF0h
                mov     ds, ax
                ;assume ds:hwUART
                mov     byte ptr ds:4, 18h
                mov     byte ptr ds:6, 18h
                mov     ax, 0DFE0h
                mov     ds, ax
                ;assume ds:hwUnkonown
                mov     byte ptr ds:0, 0
                mov     byte ptr ds:2, 0FFh
                mov     byte ptr ds:4, 0FFh
                mov     byte ptr ds:6, 0
                pop     ds
                ;assume ds:nothing
                retn
;setupUART       endp

;j_BiosEntryPoint proc far
j_BiosEntryPoint:
                jmp     SEG_MAIN:CompassPromStart
;j_BiosEntryPoint endp