SAB80C517-M16 SIEMENS [Siemens Semiconductor Group], SAB80C517-M16 Datasheet - Page 274

• Manufacturer Part Number: SAB80C517-M16
• Description: 8-Bit CMOS Single-Chip Microcontroller
• Manufacturer: SIEMENS [Siemens Semiconductor Group]

Pin Definitions and Functions (cont’d)
Symbol
PSEN
ALE
EA
P0.0 - P0.7
*
Semiconductor Group
I = Input
O = Output
52 - 59
P-LCC-84
49
50
51
Pin Number
P-MQFP-100-2
22
23
24
26 - 27,
30 - 35
275
I/O
O
O
I
I/O
*)
Function
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.
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
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
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.
SAB 80C517/80C537