14/16 0000 0000
=
Low byte of manufacturer's number
40142 0000 0000
=
Because this PIC does not generate INTs
When you want to program your own ID PAL, just work back to the
equations. First determine what ID pattern you need by reading
about the nibbles in the spec. Write down a table of ones and zeros.
Invert all of these except nibbles
00.02.40,
and
42.
Then, doing one
data line at time, write a product term for each binary zero that you
want to output from the ID PAL.
Passing CONFl&OUT*
The equations for CONFIGOUT* in this implementation make two
feedback latches in the PAL. The first latch
PRECONFIG-OUT* is set
during the bus cycle in which the processor does a write to the ad-
dress register. In fact, in this design the rising edge of
PRECONFI-
G-OUT latches the final Address value into the address latch.
The second latch outputs CONFIG-OUT*. This latch goes active after
AS* goes inactive at the end of the bus cycle in which the new ad-
dress was written. Notice that CONFIG-OUT* enables the address
latch
U1,
so
it
now provides the new address range to the compara-
tor.
CONFIG-OUT* enables the next PIC in the chain, and remains active
until a system reset or power down occurs.
TABLE
3-1
TIMING SPECIFICATIONS
Timing Requirements
for
Backplane
TIMING REQUIREMENTS FOR BACKPLANE
Num
1
2
3
4
5
6
Characteristic
AS*
UDS* LDS* Delay
Address
23-1
delay
7M(S4 RISE)
to
Data Enable during Read
7M (S4 RISE)
to
Data Valid
Data
15-0
Delay
to
Output
SLAVEIN or SLAVE
to
SLAVEOUT Delay
Min
2
2
0
0
Max
8
8
35
8
25
Unit
ns
ns
ns
ns
ns
ns
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