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 some pins,
the chosen function of the multi-function I/O pins is set by configuration options while for others the
function is set by application program control.
Buzzer
Each device in the series contains a Buzzer function, whose output pins, BZ and BZ
are
pin-shared with I/O pins PB0 and PB1. The output function of these pins is chosen via a configura
-
tion option and remains fixed after the device is programmed. Note that the corresponding bits of
the port control register, PBC, must setup the pins as outputs to enable the Buzzer outputs. If the
PBC port control register has setup the pins as inputs, then the pins will function as normal logic in
-
puts with the usual pull-high options, even if the Buzzer configuration option has been selected.
External Interrupt Input
The external interrupt pin INT
is pin-shared with the I/O pin PC0. For this pin to operate as an ex
-
ternal interrupt pin and not as a normal I/O pin the corresponding external interrupt enable bits in
the INTC interrupt control register must be correctly set. For applications not requiring an external
interrupt input, the pin can be used as a normal I/O pin, however, to do this, the external interrupt
enable bits in the INTC register must be disabled.
External Timer Clock Input
The external timer pin TMR is pin-shared with the I/O pin PC1. To configure it to operate as a timer
input, the corresponding control bits in the timer control register must be correctly set. For applica-
tions that do not require an external timer input, the pin can be used as a normal I/O pin. Note that
if used as a normal I/O pin the timer mode control bits in the timer control register must select the
timer mode (internal clock source) to prevent the I/O pin from interfering with the timer counter op-
eration.
24
Cost-Effective I/O Type MCU
V
D D
M
U
X
W a k e - u p O p t i o n
S y s t e m W a k e - u p
R e a d D a t a R e g i s t e r
C o n t r o l B i t
P u l l - H i g h O p t i o n
D a t a B u s
W r i t e C o n t r o l R e g i s t e r
C h i p R e s e t
R e a d C o n t r o l R e g i s t e r
W r i t e D a t a R e g i s t e r
D a t a B i t
P A 0 ~ P A 7
W e a k
P u l l - u p
D
Q
C K
Q
S
D
Q
C K
Q
S
PA Input/Output Ports
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