PSD511B1 datasheet(19/153 Pages) STMICROELECTRONICS

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PSD5XX Family

The PSD5XX

Architecture

(cont.)

9.1.2.1 Port A Macrocell Structure

Figure 6a shows the PA Macrocell block, which consists of 8 identical macrocells.

Each macrocell output can be connected to its own I/O pin on Port A. There are 3 user

programmable global product terms output from the GPLD’s AND ARRAY which are

shared by all the macrocells in Port A:

t PA.OE

Enable or tri-state Port A output pins

t PA.PR

Preset D flip flop in the macrocells

t PA.RE

Reset/Clear D flip flop in the macrocells

Two other inputs, CLKIN and MACRO-RST, are used as clock and clear inputs to the D flip

flop. The CLKIN comes directly from the CLKIN input pin. The MACRO-RST is the same as

the Reset input pin except it is user configurable.

The circuit of a Port A Macrocell is shown in Figure 7. There are 6 product terms from the

GPLD’s AND ARRAY as inputs to the macrocell. Users can select the polarity of the output,

and configure the macrocell to operate as:

t Registered Output

Select output from D flip flop

t Combinatorial Output

Select output from OR gate

t GPLD Input

Use Port A pin as dedicated input

t GPLD Output

Use Port A pin as dedicated output

t GPLD I/O

Use Port A pin as bidirectional pin

t Macrocell Feedback

from the combinatorial output, to expand the number of product terms available to

another macrocell.

In case of "Buried Feedback", where the output of the macrocell is not connected to a

Port A pin, Port A can be configured to perform other user defined I/O functions.

The two global product terms assigned for asynchronous clear (PA.RE) and preset (PA.PR)

are mainly for proper Port A Macrocell initialization. The macrocell flip-flop can also be

cleared during reset by MACRO-RST, if such an option is chosen. The clock source is

always the input clock CLKIN.

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