C515A_9708 Datasheet, PDF (13/182 Pages) Siemens Semiconductor Group – 8-Bit CMOS Microcontroller

Introduction
C515A
Table 1-1
Pin Definitions and Functions (cont’d)
Symbol
XTAL2
XTAL1
P2.0-P2.7
PSEN
ALE
*) I = Input
O = Output
Pin Number
(P-MQFP-80)
36
37
38-45
47
48
I/O*) Function
– XTAL2
Input to the inverting oscillator amplifier and input to the
internal clock generator circuits. To drive the device from
an external clock source, XTAL2 should be driven, while
XTAL1 is left unconnected. Minimum and maximum
high and low times as well as rise/fall times specified in
the AC characteristics must be observed.
– XTAL1
Output of the inverting oscillator amplifier.
I/O Port 2
is an 8-bit quasi-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 _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 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.
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 periods,
except during external data memory accesses. The
signal remains high during internal program execution.
O The Address Latch Enable
output is used for latching the address into external
memory during normal operation. It is activated every six
oscillator periods, except during an external data
memory access. ALE can be switched off when the
program is executed internally.
Semiconductor Group
1-8
1997-08-01