PSD835G2 datasheet(59/102 Pages) STMICROELECTRONICS

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PSD835G2

I/O PORTS

There are seven programmable I/O ports: Ports A,

B, C, D, E and F. Each of the ports is eight bits ex-

cept for Port D, which is 4 bits. Each port pin is in-

dividually user-configurable, thus allowing multiple

functions per port. The ports are configured using

PSDsoft or by the MCU writing to on-chip registers

in the CSIOP space.

The topics discussed in this section are:

■

General Port architecture

■

Port operating modes

■

Port Configuration Registers (PCR)

■

Port Data Registers

■

Individual Port functionality.

General Port Architecture

The general architecture of the I/O Port block is

shown in Figure 26., page 60. Individual Port ar-

chitectures are shown in Figure 28., page 66 to

Figure 30., page 69. In general, once the purpose

for a port pin has been defined, that pin is no long-

er available for other purposes. Exceptions are

noted.

As shown in Figure 26., page 60, the ports contain

an output multiplexer whose select signals are

driven by the configuration bits in the Control Reg-

isters (Ports E, F and G only) and PSDsoft Config-

uration. Inputs to the multiplexer include the

following:

–

Output data from the Data Out register

–

Latched address outputs

–

CPLD macrocell output

–

External Chip Select (ECS0-ECS2) from the

CPLD.

The Port Data Buffer (PDB) is a tri-state buffer that

allows only one source at a time to be read. The

Port Data Buffer (PDB) is connected to the Internal

Data Bus for feedback and can be read by the

MCU. The Data Out and macrocell outputs, Direc-

tion and Control Registers, and port pin input are

all connected to the Port Data Buffer (PDB).

The Port pin’s tri-state output driver enable is con-

trolled by a two input OR gate whose inputs come

from the CPLD AND Array enable product term

and the Direction Register. If the enable product

term of any of the Array outputs is not defined and

that port pin is not defined as a CPLD output in the

PSDabel file, then the Direction Register has sole

control of the buffer that drives the port pin.

The contents of these registers can be altered by

the MCU. The Port Data Buffer (PDB) feedback

path allows the MCU to check the contents of the

registers.

Ports A, B, and C have embedded Input Macro-

cells (IMC). The Input Macrocells (IMC) can be

configured as latches, registers, or direct inputs to

the PLDs. The latches and registers are clocked

by Address Strobe (ALE/AS, PD0) or a product

term from the PLD AND Array. The outputs from

the Input Macrocells (IMC) drive the PLD input bus

and can be read by the MCU. See Input Macro-

cells (IMC), page 46.

Port Operating Modes

The I/O Ports have several modes of operation.

Some modes can be defined using PSDabel,

some by the MCU writing to the Registers in

CSIOP space, and some by both. The modes that

can only be defined using PSDsoft must be pro-

grammed into the device and cannot be changed

unless the device is reprogrammed. The modes

that can be changed by the MCU can be done so

dynamically at run-time. The PLD I/O, Data Port,

Address Input, Peripheral I/O and MCU Reset

modes are the only modes that must be defined

before programming the device. All other modes

can be changed by the MCU at run-time.

Table 35., page 61 summarizes which modes are

available on each port. Table 38., page 64 shows

how and where the different modes are config-

ured. Each of the port operating modes are de-

scribed in the following sections.

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