PSD4235G2 datasheet(37/89 Pages) STMICROELECTRONICS

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PSD4235G2

(OMC). For example, suppose McellA0-McellA3

are being used for a state machine. You would not

want a MCU write to McellA to overwrite the state

machine registers. Therefore, you would want to

load the Mask Register for McellA (Mask Macro-

cell A) with the value 0Fh.

The Output Enable of the OMC. The

Output

Macrocells (OMC) can be connected to an I/O port

pin as a PLD output. The output enable of each

port pin driver is controlled by a single product

term from the AND Array, ORed with the Direction

up if no output enable equation is defined and if

the pin is declared as a PLD output in PSDsoft Ex-

press.

If the Output Macrocell (OMC) output is declared

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

the PSDabel file, then 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.

Input Macrocells (IMC). The CPLD has 24 Input

Macrocells (IMC), one for each pin on Ports A, B,

and C. The architecture of the Input Macrocells

(IMC) is shown in Figure 16. The Input Macrocells

(IMC) 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 Input Macrocells (IMC) can

be read by the MCU 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 Input

Macrocells (IMC). Port inputs 3-0 can be con-

trolled by one product term and 7-4 by another.

Configurations for the Input Macrocells (IMC) are

specified by PSDsoft Express (see Application

Note

AN1171). Outputs of the Input Macrocells

(IMC) can be read by the MCU via the IMC buffer.

See the section entitled “I/O Ports”, on page 50.

Input Macrocells (IMC) can use Address Strobe

(ALE/AS, PD0) to latch address bits higher than

A15. Any latched addresses are routed to the

PLDs as inputs.

Input Macrocells (IMC) are particularly useful with

handshaking communication applications where

two processors pass data back and forth through

a common mailbox. Figure 18 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 Input Mac-

rocells (IMC) and the Master can then read the In-

put Macrocells (IMC) directly.

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

are product terms that are derived from the Slave

MCU inputs Read Strobe (RD, CNTL1), Write

Strobe (WR/WRL, CNTL0), and Slave_CS.

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