B2000 System Bus Loading

                             by Dave Haynie


	In this document, I use the following numbers and notation for
standard load and drive values:

                           From A2000              To A2000
Type                     (IC input load)       (IC output drive)

F-Driver  TTL           FD   20uA   @ 2.7V     fd   2.0V @ -15mA     
                             -1.6mA @ 0.5V          0.5V @ 64mA
F-Series  TTL           F    20uA   @ 2.7V     f    2.7V @ -1mA
                             -0.6mA @ 0.5V          0.5V @ 20mA
LS-Driver TTL           LSD  20uA   @ 2.7V     lsd  2.0V @ -15mA
                             -0.4mA @ 0.4V          0.5V @ 24mA
LS-Series TTL           LS   20uA   @ 2.7V     ls   2.7V @ -400uA
                             -0.4mA @ 0.4V          0.5V @ 8mA
MOS                     MOS  10uA   @ 2.4V     mos  2.4V @ -200uA
                             -10uA  @ 0.4V          0.4V @ 3.2mA
Open Collector                                 oc   FROM RESISTOR
                                                    0.5V @ 8mA

Any lesser input load can be used on a signal in place of a greater load or
equivalent load.  Varying the number of load elements while still meeting the
DC loading criteria can be done if necessary, but it is not a good idea, as
it can still exceed the expected capacitive loading on the signal.

A final type of drive is the open collector (oc).  Some PIC outputs must
be open collector, as they are in a wired-or configuration with the same
output from other PICs or motherboard signals.

	Most of the system bus signals provide a standard drive to their
respective connectors.  If your drivers can meet the input specification,
don't worry about what is actually required.  However, even if your loading
doesn't exceed the specified drive capacity of slot signal mentioned above,
consult the following chart for specific signals that may provide less drive
than a standard signal of that type.  Signals that match the STANDARD loading
are not separately listed.

Named           DIR          Expansion     Coprocessor   Video
Signals                     Slots (each)      Slot       Slot

STANDARD         I             2F             1F          1F
STANDARD         O            10f            10f         10f
/DTACK           I             1F             1F
                 O            10f            10f
/OVR             O             oc             oc
XRDY             O             oc             oc
/INT2            O             oc             oc
/INT6            O             oc             oc
/EINT1           O             oc
/EINT4           O             oc
/EINT5           O             oc
/EINT7           O             oc
/SLAVEn          O             2f
/CFGOUTn         O             2f
/COPCFG          O                            2f
E Clock          I             1F             1F
7MHz Clock       I             1F             1F
/BEER            I             1F             1F
                 O             oc             oc
/VPA             I             1F             1F
                 O             oc             oc
/VMA             I             1F             1F
                 O            10f             10f
/RST             I             1F             1F
                 O             oc             oc
/HLT             I             1F             1F
                 O             oc             oc
/OWN             O             oc
/BRn             O             2f
/CBR             I                            2F
                 O                            2f
/CBG             I                            2F
                 O                            2f
/BGACK           I             1F             1F
                 O             oc             oc
/BOSS            O                            2f
XCLK             O                                        2f
/XCLKEN          O                                        2f