C511 Datasheet, PDF (10/43 Pages) Siemens Semiconductor Group – 8-Bit CMOS Microcontroller

C511 / C513
Table 3
Pin Definitions and Functions (cont’d)
Symbol
XTAL1
P2.0-P2.7
PSEN
RESET
Pin Number I/O*) Function
P-LCC- P-MQFP-
44
44
21
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.
24-31 18-25
I/O Port 2
is a bidirectional I/O port with internal pullup resistors.
Port 2 pins that have 1s 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_IL, in the DC 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 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.
32
26
O The Program Store Enable
output is a control signal that enables the external
program memory to the bus during external fetch
operations. It is activated every six oscillator periodes
except during external data memory accesses. Remains
high during internal program execution.
10
4
I
RESET
A high level on this pin for two machine cycles while the
oscillator is running resets the device. An internal resistor
to V_SS permits power-on reset using only an external
capacitor to V_CC.
*) I = Input
O = Output
Semiconductor Group
10