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C515C Datasheet, PDF (11/69 Pages) Siemens Semiconductor Group – 8-Bit CMOS Microcontroller
C515C
Table 1
Pin Definitions and Functions (cont’d)
Symbol
PSEN
ALE
EA
P0.0-P0.7
P5.0-P5.7
*) I = Input
O = Output
Pin Number
P-MQFP-80
47
48
49
52-59
67-60
I/O*) Function
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.
I
External Access Enable
When held high, the C515C executes instructions always
from the internal ROM. When held low, the C515C
fetches all instructions from external program memory.
I/O Port 0
is an 8-bit open-drain bidirectional I/O port.
Port 0 pins that have 1's written to them float, and in that
state can be used as high-impedance inputs.
Port 0 is also the multiplexed low-order address and data
bus during accesses to external program and data
memory. In this application it uses strong internal pullup
resistors when issuing 1's.
Port 0 also outputs the code bytes during program
verification in the C515C. External pullup resistors are
required during program verification.
I/O Port 5
is an 8-bit quasi-bidirectional I/O port with internal pullup
resistors. Port 5 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 5 pins being
externally pulled low will source current (I IL, in the DC
characteristics) because of the internal pullup resistors.
Port 5 can also be switched into a bidirectional mode, in
which CMOS levels are provided. In this bidirectional
mode, each port 5 pin can be programmed individually as
input or output.
Semiconductor Group
11
1997-07-01