PSD813F2 datasheet(53/110 Pages) STMICROELECTRONICS

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PSD8XX Family

PSD835G2

The

PSD835G2

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 24. Individual Port architectures

are shown in Figures 26 through 28. 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 24, 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 CPLD Micro

⇔Cell output

t External Chip Select from CPLD.

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 Port pin’s tri-state output driver enable is controlled 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 are 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 microcontroller. The PDB feedback

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

Ports A, B, and C have embedded Input Micro

⇔Cells (IMCs). The IMCs can be configured

as latches, registers, or direct inputs to the PLDs. The latches and registers are clocked by

the address strobe (AS/ALE) or a product term from the PLD AND array. The outputs from

the IMCs drive the PLD input bus and can be read by the microcontroller. Refer to the IMC

subsection of the PLD section.

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