Cirrus Logic CRYSTAL LAN CS890, Technical Reference Manual, Page: 30 / 80

30 AN83REV1
CS8900 Technical Reference Manual
writes to PacketPage base a 040h
to program values for Q[23:20], the
CS8900 then shifts that data serially in to
the PAL or GAL. This makes
ADD_VALID signal active.
From this point onwards LA[23:20] are
monitored whenever ALE is active (HIGH).
When the decode logic finds a match,
CHIPSEL_b signal is asserted. This signal
remains asserted until ALE becomes active
and the LA[23:20] do not match with
Q[23:20]. The internal decoder of the
CS8900 is active only when CHIPSEL_b is
active (LOW).
Figure 2.3.2 shows a simple PALASMTM
program for the 16R4 PAL that is used in
the design shown in Figure 2.3.1.
1
11
2
3
4
5
6
7
8
9
CLK
G
10
11
12
13
14
15
16
17
I/00
I/01
I/02
I/03
12
13
18
19
14
15
16
17
00
01
02
03
CHIPSEL_B (CS8900 Pin7)
PAL16R4
ELCS
EEDOUT
BALE
LA23
LA22
LA21
LA20
RESET
EE_SK
(CS8900 Pin2)
CS8900 Pin5)
(ISA B28)
(ISA C02)
(ISA C03)
(ISA C04)
(ISA C05)
(ISA B02)
(CS8900 Pin 4)
Figure 2.3.1 PAL Decode of LA[20-23]