UPSD325X datasheet(125/176 Pages) STMICROELECTRONICS

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µPSD325X DEVICES

Product Term Allocator

The CPLD has a Product Term Allocator. PSDsoft

uses the Product Term Allocator to borrow and

place product terms from one macrocell to anoth-

er. The following list summarizes how product

terms are allocated:

McellAB0-McellAB7 all have three native

product terms and may borrow up to six more

McellBC0-McellBC3 all have four native product

terms and may borrow up to five more

McellBC4-McellBC7 all have four native product

terms and may borrow up to six more.

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.

If an equation requires more product terms than

are available to it, then “external” product terms

are required, which consume other Output Macro-

cells (OMC). If external product terms are used,

extra delay is added for the equation that required

the extra product terms.

This is called product term expansion. PSDsoft

Express performs this expansion as needed.

Loading and Reading the Output Macrocells

(OMC). The Output Macrocells (OMC) block oc-

cupies a memory location in the MCU address

space, as defined by the CSIOP block (see the

section entitled “I/O PORTS (PSD MODULE),” on

page 127). The flip-flops in each of the 16 Output

Macrocells (OMC) can be loaded from the data

bus by a MCU. Loading the Output Macrocells

(OMC) with data from the MCU takes priority over

internal functions. As such, the preset, clear, and

clock inputs to the flip-flop can be overridden by

the MCU. The ability to load the flip-flops and read

them back is useful in such applications as load-

able counters and shift registers, mailboxes, and

handshaking protocols.

Data can be loaded to the Output Macrocells

(OMC) on the trailing edge of WRITE Strobe (WR,

edge loading) or during the time that WRITE

Strobe (WR) is active (level loading). The method

of loading is specified in PSDsoft Express Config-

uration.

Figure 61. 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

MCU DATA BUS

D [ 7:0]

DIRECTION

CLEAR (.RE)

PROGRAMMABLE

FF (D / T/JK /SR)

ENABLE (.OE)

PRESET(.PR)

MACROCELL CS

AI06617

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