SAB80C517 Datasheet, PDF (12/61 Pages) Siemens Semiconductor Group – 8-Bit CMOS Single-Chip Microcontroller

SAB 80C517/80C537
Pin Definitions and Functions (cont’d)
Symbol
Pin Number
I/O ^*) Function
P-LCC-84 P-MQFP-100-2
PSEN
49
22
ALE
50
23
EA
51
24
P0.0 - P0.7 52 - 59
26 - 27,
30 - 35
* _{I = Input}
O = Output
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
pro-gram 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 periodes except during an
external data memory access
I
External Access Enable
When held at high level, instructions
are fetched from the internal ROM
when the PC is less than 8192. When
held at low level, the SAB 80C517
fetches all instructions from external
program memory. For the SAB 80C537
this pin must be tied low
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 or data memory. In
this application it uses strong internal
pull-up resistors when issuing 1 s.
Port 0 also outputs the code bytes
during program verification in the
SAB 83C517. External pull-up resistors
are required during program
verification.
Semiconductor Group
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