PSD4235G2 datasheet(49/93 Pages) STMICROELECTRONICS

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PSD4000 Series

Preliminary Information

The

PSD4000

Functional

Blocks

(cont.)

9.4 I/O Ports

There are seven programmable I/O ports: Ports A, B, C, D, E, F and G. Each of the ports

is eight bits except Port D, which is 4 bits. Each port pin is individually user configurable,

thus allowing multiple functions per port. The ports are configured using PSDsoft or by the

microcontroller writing to on-chip registers in the CSIOP address space.

The topics discussed in this section are:

• General Port Architecture

• Port Operating Modes

• Port Configuration Registers

• Port Data Registers

• Individual Port Functionality.

9.4.1 General Port Architecture

The general architecture of the I/O Port is shown in Figure 20. Individual Port architectures

are shown in Figures 21 through 23. In general, once the purpose for a port pin has been

defined, that pin will no longer be available for other purposes. Exceptions will be noted.

As shown in Figure 20, the ports contain an output multiplexer whose selects are driven

by the configuration bits in the Control Registers (Ports E, F and G only) and PSDsoft

Configuration. Inputs to the multiplexer include the following:

t Output data from the Data Out Register

t Latched address outputs

t GPLD outputs (External Chip Selects)

The Port Data Buffer (PDB) is a tri-state buffer that allows only one source at a time to be

read. The PDB is connected to the Internal Data Bus for feedback and can be read by the

microcontroller. The Data Out and Micro

⇔Cell outputs, Direction and Control Registers,

and port pin input are all connected to the PDB.

The contents of these registers can be altered by the microcontroller. The PDB feedback

path allows the microcontroller to check the contents of the registers.

9.4.2 Port Operating Modes

The I/O Ports have several modes of operation. Some modes can be defined using

PSDsoft, some by the microcontroller writing to the Registers in CSIOP space, and some

by both. The modes that can only be defined using PSDsoft must be programmed into the

device and cannot be changed unless the device is reprogrammed. The modes that can be

changed by the microcontroller can be done so dynamically at run-time. The PLD I/O,

Data Port, Address Input, and MCU Reset modes are the only modes that must be defined

before programming the device. All other modes can be changed by the microcontroller at

run-time.

Table 16 summarizes which modes are available on each port. Table 19 shows how and

where the different modes are configured. Each of the port operating modes are described

in the following subsections.

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