ISA (IBM) Connector Pinout vs. TI Professional Connector Pinout



TI Signal       IBM Signal      Pin     Pin     IBM Signal      TI Signal
  name             name                            name           name
---------       ----------      ---     ---     ----------      ----------
Ground          Ground          B1      A1      -I/O CH CK      NMI

RESET           RESET DRV       B2      A2      SD7             Data 7

+5 V dc         +5 V dc         B3      A3      SD6             Data 6

IR0             IRQ9            B4      A4      SD5             Data 5
 (interrupt 0)

no connection   -5 V dc         B5      A5      SD4             Data 4
 (bused)

no connection   DRQ2            B6      A6      SD3             Data 3
 (bused)

-12 V dc        -12 V dc        B7      A7      SD2             Data 2

DMA             -0WS            B8      A8      SD1             Data 1
 (CPU enable)

+12 V dc        +12 V dc        B9      A9      SD0             Data 0

Ground          Ground          B10     A10     I/O CH RDY      WAIT

AMWC            -SMEMW          B11     A11     AEN             Logic ground
 (memory write) 

MRDC            -SMEMR          B12     A12     SA19            Address 19 (MSB)
 (memory read)

AIOWC           -IOW            B13     A13     SA18            Address 18
 (I/O write)

IORC            -IOR            B14     A14     SA17            Address 17
 (I/O read)

no connection   -DACK3          B15     A15     SA16            Address 16
 (bused)

no connection   DRQ3            B16     A16     SA15            Address 15
 (bused)

no connection   -DACK1          B17     A17     SA14            Address 14
 (bused)

no connection   DRQ1            B18     A18     SA13            Address 13
 (bused)

no connection   -REFRESH        B19     A19     SA12            Address 12
 (bused)

PCLK            CLK             B20     A20     SA11            Address 11
 (5-MHz clock)

IR6             IRQ7            B21     A21     SA10            Address 10
 (interrupt 6)

IR5             IRQ6            B22     A22     SA9             Address 9
 (interrupt 5)

IR4             IRQ5            B23     A23     SA8             Address 8
 (interrupt 4)

IR2             IRQ4            B24     A24     SA7             Address 7
 (interrupt 2)

IR1             IRQ3            B25     A25     SA6             Address 6
 (interrupt 1)

no connection   -DACK2          B26     A26     SA5             Address 5
 (bused)

RFSH            TC              B27     A27     SA4             Address 4
 (refreshing)

ALE             BALE            B28     A28     SA3             Address 3
 (address latch)

+5 V dc         +5 V dc         B29     A29     SA2             Address 2

OSC             OSC             B30     A30     SA1             Address 1
 (15-MHz clock)

Ground          Ground          B31     A31     SA0             Address 0 (LSB)



Notes by pin number:

Pins B1  to B3,
     B7,
     B9  to B14,
     B28 to B29,
     B31,
     A1  to A10, and
     A12 to A31:

        All have the same function with both the IBM and TI busses although
        the terminology may differ ("AIOWC" vs. "-IOW" where IBM omits
        the "A" to indicate an advanced signal, one sent ahead of time
        to give the circuits time to prepare to carry out the operation
        and uses a preceding "-" to indicate an active low signal where
        TI uses a trailing "C" to indicate a "Complemented" (active low)
        signal or the completely different names of "NMI" and "-I/O CH CK"
        for the same function).

Pins B4,
     B21 to B25:

        Both busses use these for interrupts and they are identical as
        far as hardware is concerned.  Only the software need differ
        because different interrupts are activated and different interrupt
        vectors are used.  On the TI, these are used:
            Pin    Hardware interrupt   Interrupt vector 
            B4            IR0               INT 40h
            B21           IR6               INT 46h (disk controller)
            B22           IR5               INT 45h
            B23           IR4               INT 44h
            B24           IR2               INT 42h (communications)
            B25           IR1               INT 41h

Pin  B5:

       No -5V dc available on the TI.  You *could* plug in a card that
       took the -12V dc from pin B7 and converted it to -5V on pin B5.
       (The "bused" means that there is no connection between the TI PC
       and that pin on the bus but all of the same-numbered "bused" pins
       on the card connectors are tied together.

Pins B6,
     B15 to B19,
     B26:

       The signals on the IBM PC on these lines are all associated with
       DMA or refresh.  The TI does not use DMA and the refresh method
       differs on the TI so any IBM card that uses these features will be
       unusable on the TI.

Pins  B8,
      B27:

       The signals on thse pins differ on the IBM and on the TI
       but I don't know what conditions are necessary for either
       of the signals to be invoked or used and have seen no
       ill effects plugging in an IBM-compatable video card
       and accessing its static memory.

Pins B20,
     B30:

       These carry comparable clock signals on the TI PC and the IBM PC.
       The frequencies of the clocks differ, however, and anything that
       is timing-critical should not rely on the clocks being the same.
            Pin B20:  5 MHz on the TI, 8 to 10 MHz on the IBM PC but the
                          exact frequency is not guaranteed.
            Pin B30:  15 MHz on the TI, 14.31818 MHz on the IBM PC.


Pin  A11:

       Forced low on the TI which would disable any DMA on IBM cards.



More on the IBM PC bus can be found at:
    http://www.techfest.com/hardware/bus/isa.htm

More on the TI Professional bus can be found at ..., um, well, I can't
find anyplace unless you can find a copy of the December 1983 issue of
Byte magazine..