DSM2180F3 datasheet(30/63 Pages) STMICROELECTRONICS

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Each Macrocell may only borrow product terms

from certain other Macrocells. Product terms al-

ready in use by one Macrocell are not available for

another Macrocell. Product term allocation does

not add any propagation delay to the logic.

If an equation requires more product terms than

are available to it through product term allocation,

then “external” product terms are required, which

consumes other Output Macrocells (OMC). This is

called product term expansion and also happens

automatically in PSDsoft ExpressTM as needed.

Product tern expansion causes additional propa-

gation delay because an OMC is consumed by the

expansion and it’s output is rerouted (or fed back)

into the AND array.

You can examine the fitter report generated by

PSDsoft Express to see resulting product term al-

location and product term expansion.

Loading and Reading the Output Macrocells

(OMCs). Each of the two OMC blocks (8 OMCs

each) occupies a memory location in the DSP ad-

dress space, as defined in the csiop block

MCELLAB0-7 and MCELLBC0-7 (see Table 4).

The flip-flops in each of the 16 OMCs can be load-

ed from the data bus by a DSP. Loading the OMCs

with data from the DSP takes priority over internal

functions. As such, the preset, clear, and clock in-

puts to the flip-flop can be overridden by the DSP.

The ability to load the flip-flops and read them

back is useful in such applications as loadable

counters and shift registers, mailboxes, and hand-

shaking protocols.

Data is loaded into the Output Macrocells (OMC)

on the trailing edge of Write Strobe (WR, CNTL0).

Figure 17. CPLD Output Macrocell

Allocator

MASK

REG.

PT CLK

CLKIN

Feedback (.FB)

Port Input

MUX

POLARITY

SELECT

CLR

DIN

COMB/REG

SELECT

Port

Driver

Input

Macrocell

I/O Pin

Macrocell

Allocator

INTERNAL DATA BUS

D [ 7:0]

Direction

CLEAR (.RE)

Programmable

FF (D / T/JK /SR)

ENABLE (.OE)

PRESET(.PR)

Output Macrocell CS

AI04903B

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