C517A Datasheet, PDF (9/67 Pages) Siemens Semiconductor Group – 8-Bit CMOS Microcontroller

C517A
Table 2
Pin Definitions and Functions (cont’d)
Symbol
Pin Number I/O*) Function
P-MQFP-100
EA
24
I
External Access Enable
When held high, the C517A executes instructions from the
internal ROM as long as the PC is less than 8000H. When
held low, the C517A fetches all instructions from external
program memory. For the C517A-L this pin must be tied
low.
P0.0 - P0.7 26, 27,
30 - 35
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 C517A. External pullup resistors are required during
program verification.
HWPD
36
I
Hardware Power Down
A low level on this pin for the duration of one machine cycle
while the oscillator is running resets the C517A. A low level
for a longer period will force the part into hardware power
down mode with the pins floating. There is no internal
pullup resistor connected to this pin.
P5.0 - P5.7 44 - 37
I/O Port 5
is a quasi-bidirectional I/O port with internal pull-up
resistors. Port 5 pins that have 1 s written to them are
pulled high by the internal pull-up 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 pull-up resistors.
This port also serves the alternate function “Concurrent
Compare” and “Set/Reset Compare”. The secondary
functions are assigned to the port 5 pins as follows:
CCM0 to CCM7 P5.0 to P5.7:
concurrent compare or Set/Reset lines
*) I = Input
O = Output
Semiconductor Group
9
1997-10-01