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Pin Definitions and Functions (cont'd)
Symbol
Pin
P-LCC-68
XTAL2
39
XTAL1
40
P2.0-P2.7 41-48
Semiconductor Group
Pin
Input (I)
P-MQFP-80
Output (O)
36
37
38-45
I/O
Function
XTAL2
Input to the inverting oscillator amplifier
and input to the internal clock generator
circuits.
XTAL1
Output of the inverting oscillator amplifier.
To drive the device from an external clock
source, XTAL2 should be driven, while
XTAL1 is left unconnected. There are no
requirements on the duty cycle of the
external clock signal, since the input to the
internal clocking circuitry is divided down
by a divide-by-two flip-flop. Minimum and
maximum high and low times and rise/fall
times specified in the AC characteristics
must be observed.
*
Port 2
is an 8-bit bidirectional I/O port with
internal pullup resistors. Port 2 pins that
have 1's written to them are pulled high by
the internal pullup resistors, and in that
state can be used as inputs. As inputs,
port 2 pins being externally pulled low will
source current (I
characteristics) because of the internal
pullup resistors.
Port 2 emits the high-order address byte
during fetches from external program
memory and during accesses to external
data memory that use 16-bit addresses
(MOVX@DPTR). In this application it
uses strong internal pullup resistors when
issuing 1's. During accesses to external
data memory that use 8-bit addresses
(MOVX@Ri), port 2 issues the contents of
the P2 special function register.
223
Device Specifications
in the DC
I L,
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