SAB-C165 SIEMENS [Siemens Semiconductor Group], SAB-C165 Datasheet - Page 7

• Manufacturer Part Number: SAB-C165
• Description: C16x-Family of High-Performance CMOS 16-Bit Microcontrollers
• Manufacturer: SIEMENS [Siemens Semiconductor Group]

Pin Definitions and Functions (cont’d)
Symbol
P4.0 –
P4.7
RD
WR/
WRL
READY
ALE
EA
Semiconductor Group
Pin
No.
25 - 28,
31 - 34
25
...
34
35
36
37
38
39
Input (I)
Output (O)
I/O
O
...
O
O
O
I
O
I
Function
Port 4 is an 8-bit bidirectional I/O port. It is bit-wise
programmable for input or output via direction bits. For a pin
configured as input, the output driver is put into high-
impedance state.
In case of an external bus configuration, Port 4 can be used to
output the segment address lines:
P4.0
...
P4.7
External Memory Read Strobe. RD is activated for every
external instruction or data read access.
External Memory Write Strobe. In WR-mode this pin is
activated for every external data write access. In WRL-mode
this pin is activated for low byte data write accesses on a 16-
bit bus, and for every data write access on an 8-bit bus. See
WRCFG in register SYSCON for mode selection.
Ready Input. When the Ready function is enabled, a high
level at this pin during an external memory access will force
the insertion of memory cycle time waitstates until the pin
returns to a low level.
Address Latch Enable Output. Can be used for latching the
address into external memory or an address latch in the
multiplexed bus modes.
External Access Enable pin. A low level at this pin during and
after Reset forces the C165 to begin instruction execution out
of external memory. A high level forces execution out of the
internal ROM. The C165 must have this pin tied to ‘0’.
A16
...
A23
6
Least Significant Segment Addr. Line
...
Most Significant Segment Addr. Line
C165