80C251SB16 Datasheet, PDF (13/36 Pages) Intel Corporation – HIGH-PERFORMANCE CHMOS MICROCONTROLLER

8XC251SA/SB/SP/SQ HIGH-PERFORMANCE CHMOS MICROCONTROLLER
Table 7. Memory Signal Selections (RD1:0)
RD1:0
P1.7/CEX/
A17/WCLK
0 0 A17
0 1 P1.7/CEX4/
WCLK
1 0 P1.7/CEX4/
WCLK
1 1 P1.7/CEX4/
WCLK
P3.7/RD#/A16
PSEN#
WR#
Features
A16
A16
P3.7 only
RD# asserted
for addresses
≤ 7F:FFFFH
Asserted for
all addresses
Asserted for
all addresses
Asserted for
all addresses
Asserted for
≥ 80:0000H
Asserted for writes to
all memory locations
Asserted for writes to
all memory locations
Asserted for writes to
all memory locations
Asserted only for
writes to MCS 51
microcontroller data
memory locations.
256-Kbyte external
memory
128-Kbyte external
memory
64-Kbyte external
memory. One
additional port pin.
64-Kbyte external
memory. Compatible
with MCS 51 micro-
controllers.
PRELIMINARY
13