PSD813F2 datasheet(38/110 Pages) STMICROELECTRONICS

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PSD813F2, PSD833F2, PSD834F2, PSD853F2, PSD854F2

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Product Term Allocator

The CPLD has a Product Term Allocator. The PS-

Dabel compiler uses the Product Term Allocator to

borrow and place product terms from one macro-

cell to another. 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 occupies a

memory location in the MCU address space, as

defined by the CSIOP block (see the section enti-

tled I/O PORTS, page 51). 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 over-

ridden by the MCU. The ability to load the flip-flops

and read them back is useful in such applications

as loadable counters and shift registers, mailbox-

es, and handshaking protocols.

Data can be loaded to the Output Macrocells

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

CNTL0) (edge loading) or during the time that

Write Strobe (WR, CNTL0) is active (level load-

ing). The method of loading is specified in PSDsoft

Express Configuration.

The OMC Mask Register

There is one Mask Register for each of the two

groups of eight Output Macrocells (OMC). The

Mask Registers can be used to block the loading

of data to individual Output Macrocells (OMC).

The default value for the Mask Registers is 00h,

which allows loading of the Output Macrocells

(OMC). When a given bit in a Mask Register is set

to a 1, the MCU is blocked from writing to the as-

sociated Output Macrocells (OMC). For example,

suppose McellAB0-McellAB3 are being used for a

state machine. You would not want a MCU write to

McellAB to overwrite the state machine registers.

Therefore, you would want to load the Mask Reg-

ister for McellAB (Mask Macrocell AB) with the val-

ue 0Fh.

The Output Enable of the OMC

The Output Macrocells (OMC) block can be con-

nected to an I/O port pin as a PLD output. The out-

put enable of each port pin driver is controlled by

a single product term from the AND Array, ORed

with the Direction Register output. The pin is en-

abled upon Power-up if no output enable equation

is defined and if the pin is declared as a PLD out-

put in PSDsoft Express.

If the Output Macrocell (OMC) output is declared

as an internal node and not as a port pin output in

the PSDabel file, the port pin can be used for other

I/O functions. The internal node feedback can be

routed as an input to the AND Array.

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