PSD813F1 datasheet(41/110 Pages) STMICROELECTRONICS

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PSD813F1

Input Macrocells (IMC)

The CPLD has 24 IMCs, one for each pin on Ports

A, B, and C. The architecture of the IMC is shown

in Figure 19., page 42. The IMCs are individually

configurable, and can be used as a latch, register,

or to pass incoming Port signals prior to driving

them onto the PLD input bus. The outputs of the

IMCs can be read by the microcontroller through

the internal data bus.

The enable for the latch and clock for the register

are driven by a multiplexer whose inputs are a

product term from the CPLD AND array or the

MCU address strobe (ALE/AS). Each product term

output is used to latch or clock four IMCs. Port in-

puts 3-0 can be controlled by one product term

and 7-4 by another.

Configurations for the IMCs are specified by equa-

tions written in PSDabel (see Application Note 55).

Outputs of the IMCs can be read by the MCU via

the IMC buffer. See the I/O Port section on how to

read the IMCs.

IMCs can use the address strobe to latch address

bits higher than A15. Any latched addresses are

routed to the PLDs as inputs.

IMCs are particularly useful with handshaking

communication applications where two proces-

sors pass data back and forth through a common

mailbox. Figure 20., page 43 shows a typical con-

figuration where the Master MCU writes to the Port

A Data Out Register. This, in turn, can be read by

the Slave MCU via the activation of the “Slave-

Read” output enable product term.

The Slave can also write to the Port A IMCs and

the Master can then read the IMCs directly.

Note that the “Slave-Read” and “Slave-wr” signals

are product terms that are derived from the Slave

MCU inputs RD, WR, and Slave_CS.

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