C501 Datasheet, PDF (10/48 Pages) Siemens Semiconductor Group – 8-Bit CMOS Microcontroller

C501
Table 1
Pin Definitions and Functions (cont’d)
Symbol
Pin Number
I/O*) Function
P-LCC-44 P-DIP-40 P-MQFP-44
XTAL2
20
18
14
– XTAL2
Output of the inverting oscillator
amplifier.
XTAL1
21
19
15
– XTAL1
Input to the inverting oscillator amplifier
and input to the internal clock generator
circuits.
To drive the device from an external
clock source, XTAL1 should be driven,
while XTAL2 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 as well as rise fall times specified
in the AC characteristics must be
observed.
P2.0 – P2.7 24–31 21–28 18–25
I/O Port 2
is a quasi-bidirectional I/O port with
internal pull-up resistors. Port 2 pins that
have 1s written to them are pulled high
by the internal pull-up resistors, and in
that state they can be used as inputs. As
inputs, port 2 pins being externally pulled
low will source current (I_IL, in the DC
characteristics) because of the internal
pull-up 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
pull-up resistors when issuing 1s. During
accesses to external data memory that
use 8-bit addresses (MOVX @Ri), port
2 issues the contents of the P2 special
function register.
*) I = Input
O = Output
Semiconductor Group
10
1997-04-01