PSD4235G2-12UT datasheet(77/124 Pages) STMICROELECTRONICS

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PSD4235G2V

I/O ports

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19.3

MCU I/O mode

In the MCU I/O mode, the MCU uses the PSD Ports to expand its own I/O ports. By setting

up the CSIOP space, the ports on the PSD are mapped into the MCU address space. The

addresses of the ports are listed in Table 5.

A port pin can be put into MCU I/O mode by writing a ’0’ to the corresponding bit in the

Control register (for Ports E, F and G). The MCU I/O direction may be changed by writing to

the corresponding bit in the Direction register, or by the output enable product term (see

Section 19.2: Port operating modes). When the pin is configured as an output, the content of

the Data Out register drives the pin. When configured as an input, the MCU can read the

port input through the Data In buffer (see Figure 26).

Ports A, B and C do not have Control registers, and are in MCU I/O mode by default. They

can be used for PLD I/O if they are specified in PSDsoft Express.

19.4

PLD I/O mode

The PLD I/O Mode uses a port as an input to the CPLD’s input macrocells (IMC), and/or as

an output from the CPLD’s output macrocells (OMC). The output can be tri-stated with a

control signal. This output enable control signal can be defined by a product term from the

PLD, or by resetting the corresponding bit in the Direction register to ’0’. The corresponding

bit in the Direction register must not be set to ’1’ if the pin is defined for a PLD input signal in

PSDsoft Express. The PLD I/O mode is specified in PSDsoft Express by declaring the port

pins, and then specifying an equation in PSDsoft Express.

19.5

Address Out mode

For MCUs with a multiplexed address/data bus, Address Out mode can be used to drive

latched addresses onto the port pins. These port pins can, in turn, drive external devices.

Either the output enable or the corresponding bits of both the Direction register and Control

MCU at run-time. See Table 40 for the address output pin assignments on Ports E, F and G

for various MCUs.

Note:

Do not drive address signals with Address Out Mode to an external memory device if it is

intended for the MCU to Boot from the external device. The MCU must first Boot from PSD

memory so the Direction and Control register bits can be set.

Table 38.

Port operating modes

Port Mode

Port A

Port B

Port C

Port D

Port E

Port F

Port G

MCU I/O

Yes

PLD I/O

McellA outputs

McellB outputs

Additional Ext. CS outputs

PLD inputs

Yes

Address Out

Yes (A7 - 0)

or (A15 - 8)

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