PSD833F2 datasheet(69/128 Pages) STMICROELECTRONICS

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PSD8XXFX

I/O ports

Doc ID 7833 Rev 7

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16.3

MCU I/O mode

In the MCU I/O mode, the MCU uses the I/O ports block 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 8.

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

Control register. 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 16.8: Peripheral

I/O mode). 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 25).

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

be used for PLD I/O if equations are written for them in PSDabel.

16.4

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

PSDabel. The PLD I/O mode is specified in PSDabel by declaring the port pins, and then

writing an equation assigning the PLD I/O to a port.

16.5

Address Out mode

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

latched addresses on to 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 22 for the address output pin assignments on ports A and B for

various MCUs.

For non-multiplexed 8-bit bus mode, address signals (A7-A0) are available to port B in

Address Out mode.

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 20.

Port operating modes

Port mode

Port A

Port B

Port C

Port D

MCU I/O

Yes

PLD I/O

McellAB outputs

McellBC outputs

Additional Ext. CS outputs

PLD inputs

Yes

Obsolete

Product(s)

- Obsolete

Product(s)

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