Intel 8XC251SA - Page 393

B-1
APPENDIX B
SIGNAL DESCRIPTIONS
This appendix provides reference information for the external signals of the 8XC251Sx. pin as-
signments are shown in Figures B-1 (PLCC package) and B-2 (DIP package) and are listed by
functional category in Table B-1.
Table B-2 describes each of the signals. It lists the signal type (input, output, power, or ground)
and the alternative functions of multifunction pins. Table B-3 shows how configuration bits
RD1:0 (referred to in Table B-2) configure the A17, A16. RD#, WR# and PSEN# pins for exter-
nal memory accesses.
Figure B-1. 8XC251SA, SB, SP, SQ 44-pin PLCC Package
AD4 / P0.4
AD5 / P0.5
AD6 / P0.6
AD7 / P0.7
EA# / V
PP 
V
SS2

ALE / PROG#
PSEN#
A15 / P2.7
A14 / P2.6
A13 / P2.5
P1.4 / CEX1 P1.3 / CEX0 P1.2 / ECI P1.1 / T2EX P1.0 / T2 V
SS1

V
CC

AD0 / P0.0 AD1 / P0.1  AD2 / P0.2  AD3 / P0.3
A4205-02
P1.5 / CEX2
P1.6 / CEX3 / WAIT#
P1.7 / CEX4 / A17 / WCLK
RST
P3.0 / RXD
V
CC2

P3.1 / TXD
P3.2 / INT0#
P3.3 / INT1#
P3.4 / T0
P3.5 / T1
39
38
37
36
35
34
33
32
31
30
29
8XC251SA
8XC251SB
8XC251SP
8XC251SQ
View of component as
mounted on PC board
7
8
9
10
11
12
13
14
15
16
17
P3.6 / WR#
P3.7 / RD# / A16
XTAL2 XTAL1
V
SS

V
SS2

A8 / P2.0 A9 / P2.1
A10 / P2.2 A11 / P2.3 A12 / P2.4
18 19 20 21 22 23 24 25 26 27 28
6 5 4 3 2 1
44 43 42 41 40