PSD813F1 datasheet(59/110 Pages) STMICROELECTRONICS

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PSD813F1

Port Data Registers

The Port Data Registers, shown in Table 27, are

used by the MCU to write data to or read data from

the ports. Table 27 shows the register name, the

ports having each register type, and MCU access

for each register type. The registers are described

below.

Data In

Port pins are connected directly to the Data In buff-

er. In MCU I/O input mode, the pin input is read

through the Data In buffer.

Data Out Register

Stores output data written by the MCU in the MCU

I/O output mode. The contents of the Register are

driven out to the pins if the Direction Register or

the output enable product term is set to ‘1.’ The

contents of the register can also be read back by

the MCU.

Output Macrocells (OMC)

The CPLD Output Macrocells (OMC) occupy a lo-

cation in the microcontroller’s address space. The

microcontroller can read the output of the OMCs.

If the Mask Macrocell Register bits are not set,

writing to the Macrocell loads data to the Macrocell

flip flops. See the section entitled PLD’S, page 34.

Mask Macrocell Register

Each Mask Register bit corresponds to an OMC

flip flop. When the Mask Register bit is set to a “1”,

loading data into the OMC flip flop is blocked. The

default value is “0” or unblocked.

Input Macrocells (IMC)

The IMCs can be used to latch or store external in-

puts. The outputs of the IMCs are routed to the

PLD input bus, and can be read by the microcon-

troller.

Refer

the

section

entitled

PLD’S, page 34 for a detailed description.

Table 27. Port Data Registers

Port

MCU Access

Data In

A,B,C,D

READ – input on pin

Data Out

A,B,C,D

WRITE/READ

Output Macrocell

A,B,C

READ – outputs of macrocells

WRITE – loading macrocell flip-flop

Mask Macrocell

A,B,C

WRITE/READ – prevents loading into a given

macrocell

Input Macrocell

A,B,C

READ – outputs of the Input Macrocells

Enable Out

A,B,C

READ – the output enable control of the port driver

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