C167CS datasheet(137/517 Pages) INFINEON

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C167CS

Derivatives

Parallel Ports

User’s Manual

7-10

V2.0, 2000-07

If an alternate output function of a pin is to be used, the direction of this pin must be

programmed for output (DPx.y = ‘1’), except for some signals that are used directly after

reset

and

are

configured

automatically.

Otherwise

the

remains

the

high-impedance state and is not effected by the alternate output function. The respective

port latch should hold a ‘1’, because its output is combined with the alternate output data.

X-Peripherals (peripherals connected to the on-chip XBUS) control their associated IO

pins directly via separate control lines.

If an alternate input function of a pin is used, the direction of the pin must be

programmed for input (DPx.y = ‘0’) if an external device is driving the pin. The input

direction is the default after reset. If no external device is connected to the pin, however,

one can also set the direction for this pin to output. In this case, the pin reflects the state

of the port output latch. Thus, the alternate input function reads the value stored in the

port output latch. This can be used for testing purposes to allow a software trigger of an

alternate input function by writing to the port output latch.

On most of the port lines, the user software is responsible for setting the proper direction

when using an alternate input or output function of a pin. This is done by setting or

clearing the direction control bit DPx.y of the pin before enabling the alternate function.

There are port lines, however, where the direction of the port line is switched

automatically. For instance, in the multiplexed external bus modes of PORT0, the

direction must be switched several times for an instruction fetch in order to output the

addresses and to input the data. Obviously, this cannot be done through instructions. In

these cases, the direction of the port line is switched automatically by hardware if the

alternate function of such a pin is enabled.

To determine the appropriate level of the port output latches check how the alternate

data output is combined with the respective port latch output.

There is one basic structure for all port lines with only an alternate input function. Port

lines with only an alternate output function, however, have different structures due to the

way the direction of the pin is switched and depending on whether the pin is accessible

by the user software or not in the alternate function mode.

All port lines that are not used for these alternate functions may be used as general

purpose IO lines. When using port pins for general purpose output, the initial output

value should be written to the port latch prior to enabling the output drivers, in order to

avoid undesired transitions on the output pins.

This applies to single pins as well as to pin groups (see examples below).

C167CS Datasheet(PDF) 137 Page - Infineon Technologies AG

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