Pin-Shared Functions - Holtek HT67F2350 Manual

HT67F2350/HT67F2360
HT67F2370/HT67F2390
Advanced A/D Flash MCU with LCD & EEPROM

Pin-shared Functions

The flexibility of the microcontroller range is greatly enhanced by the use of pins that have more
than one function. Limited numbers of pins can force serious design constraints on designers but by
supplying pins with multi-functions, many of these difficulties can be overcome. For these pins, the
desired function of the multi-function I/O pins is selected by a series of registers via the application
program control.
Pin-shared Function Selection Registers
The limited number of supplied pins in a package can impose restrictions on the amount of functions
a certain device can contain. However by allowing the same pins to share several different functions
and providing a means of function selection, a wide range of different functions can be incorporated
into even relatively small package sizes. Each device includes Port "x" output function Selection
register "n", labeled as PxSn, and Input Function Selection register, labeled as IFSn, which can
select the desired functions of the multi-function pin-shared pins.
When the pin-shared input function is selected to be used, the corresponding input and output
functions selection should be properly managed. For example, if the I
corresponding output pin-shared function should be configured as the SDI/SDA function by
configuring the PxSn register and the SDA signal input should be properly selected using the IFSn
register. However, if the external interrupt function is selected to be used, the relevant output pin-
shared function should be selected as an I/O function and the interrupt input signal should be
selected.
The most important point to note is to make sure that the desired pin-shared function is properly
selected and also deselected. For most pin-shared functions, to select the desired pin-shared function,
the pin-shared function should first be correctly selected using the corresponding pin-shared control
register. After that the corresponding peripheral functional setting should be configured and then the
peripheral function can be enabled. However, a special point must be noted for some digital input
pins, such as INTn, xTCKn, xTPnI, etc, which share the same pin-shared control configuration with
their corresponding general purpose I/O functions when setting the relevant pin-shared control bit
fields. To select these pin functions, in addition to the necessary pin-shared control and peripheral
functional setup aforementioned, they must also be setup as an input by setting the corresponding bit
in the I/O port control register. To correctly deselect the pin-shared function, the peripheral function
should first be disabled and then the corresponding pin-shared function control register can be
modified to select other pin-shared functions.
Rev. 1.60 117
C SDA line is used, the
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May 16, 2019