Macrocell
The macrocell consists of a storage element, routing resources, a clock multiplexer, and initialization
control. The macrocell has two fundamental modes: synchronous and asynchronous (Figure 5). The mode
chosen only affects clocking and initialization in the macrocell.
Power-Up
Reset
PAL-Block
Initialization
Product Terms
Common PAL-block resource
Individual macrocell resources
From Logic Allocator
From
PAL-Clock
Generator
Block CLK0
Block CLK1
Block CLK2
Block CLK3
SWAP
AP AR
D/T/L Q
a. Synchronous mode
To Output and Input
Switch Matrices
17466G-009
Individual
Initialization
Product Term
Power-Up
Reset
SWAP
From Logic
Allocator
From PAL-Block
Clock Generator
Individual Clock
Product Term
Block CLK0
Block CLK1
AP AR
D/T/L Q
b. Asynchronous mode
Figure 5. Macrocell
To Output and Input
Switch Matrices
17466G-010
In either mode, a combinatorial path can be used. For combinatorial logic, the synchronous mode will
generally be used, since it provides more product terms in the allocator.
10
ispMACH 4A Family