These devices can address up to 64 Kbytes of external program data memory
The Intel 8XC51RA 8XC51RB 8XC51RC is a single-chip control-oriented microcontroller which is fabricated
on Intel’s reliable CHMOS III-E technology Being a member of the MCS 51 family of controllers the
8XC51RA 8XC51RB 8XC51RC uses the same powerful instruction set has the same architecture and is pin-
for-pin compatible with the existing MCS 51 family of products The 8XC51RA 8XC51RB 8XC51RC is an
enhanced version of the 8XC52 8XC54 8XC58 The added features make it an even more powerful microcon-
troller for applications that require 512 bytes of on-chip data RAM and dedicated hardware WatchDog Timer
with reset-out features
Throughout this document 8XC51RX will refer to the 8XC51RA 8XC51RB and 8XC51RC unless information
applies to a specific device
For a detailed description of 8XC51RA RB RC refer to the 8XC51RA RB RC Hardware Description order
number 272668
Other brands and names are the property of their respective owners
Information in this document is provided in connection with Intel products Intel assumes no liability whatsoever including infringement of any patent or
copyright for sale and use of Intel products except as provided in Intel’s Terms and Conditions of Sale for such products Intel retains the right to make
changes to these specifications at any time without notice Microcomputer Products may have minor variations to this specification known as errata
COPYRIGHT
INTEL CORPORATION 1995
December 1995
Order Number 272659-002
8XC51RA RB RC
Table 1 Proliferations Options
80C51RA
83C51RA
87C51RA
83C51RB
87C51RB
83C51RC
87C51RC
Standard
1
X
X
X
X
X
X
X
-1
X
X
X
X
X
X
X
-20
X
X
X
X
X
X
X
-24
X
X
X
X
X
X
X
NOTES
1 35
-1 3 5
-20 3 5
-24 3 5
MHz
MHz
MHz
MHz
to
to
to
to
12
16
20
24
MHz
MHz
MHz
MHz
5V
5V
5V
5V
g
20%
g
20%
g
20%
g
10%
272659 –4
Figure 1 8XC51RX Block Diagram
2
8XC51RA RB RC
PROCESS INFORMATION
This device is manufactured on P629 5 a CHMOS
III-E process Additional process and reliability infor-
mation is available in the
Intel® Quality System
Handbook.
PACKAGES
Part
8XC51RX
8XC51RX
8XC51RX
Prefix
P
N
S
Package Type
40-Pin Plastic DIP (OTP)
44-Pin PLCC (OTP)
44-Pin QFP (OTP)
272659 –2
PLCC
272659 –1
DIP
272659– 3
Do not connect reserved pins
QFP
Figure 2 Pin Connections
3
8XC51RA RB RC
LS TTL inputs Port 2 pins that have 1’s written to
them are pulled high by the internal pullups and in
that state can be used as inputs As inputs Port 2
pins that are externally pulled low will source current
(I
IL
on the data sheet) because of the internal pull-
ups
Port 2 emits the high-order address byte during
fetches from external Program Memory and during
accesses to external Data Memory that use 16-bit
addresses (MOVX DPTR) In this application it
uses strong internal pullups when emitting 1’s Dur-
ing accesses to external Data Memory that use 8-bit
addresses (MOVX Ri) Port 2 emits the contents of
the P2 Special Function Register
Some Port 2 pins receive the high-order address bits
during EPROM programming and program verifica-
tion
Port 3
Port 3 is an 8-bit bidirectional I O port with
internal pullups The Port 3 output buffers can drive
LS TTL inputs Port 3 pins that have 1’s written to
them are pulled high by the internal pullups and in
that state can be used as inputs As inputs Port 3
pins that are externally pulled low will source current
(I
IL
on the data sheet) because of the pullups
Port 3 also serves the functions of various special
features of the 8051 Family as listed below
Port Pin
P3 0
P3 1
P3 2
P3 3
P3 4
P3 5
P3 6
P3 7
Alternate Function
RXD (serial input port)
TXD (serial output port)
INT0 (external interrupt 0)
INT1 (external interrupt 1)
T0 (Timer 0 external input)
T1 (Timer 1 external input)
WR (external data memory write strobe)
RD (external data memory read strobe)
PIN DESCRIPTIONS
V
CC
Supply voltage
V
SS
Circuit ground
V
SS1
Secondary ground (not on DIP) Provided to
reduce ground bounce and improve power supply
by-passing
NOTE
This pin is not a substitute for the V
SS
pin (pin 22)
(Connection not necessary for proper operation )
Port 0
Port 0 is an 8-bit open drain bidirectional
I O port As an output port each pin can sink several
LS TTL inputs Port 0 pins that have 1’s written to
them float and in that state can be used as high-im-
pedance inputs
Port 0 is also the multiplexed low-order address and
data bus during accesses to external Program and
Data Memory In this application it uses strong inter-
nal pullups when emitting 1’s and can source and
sink several LS TTL inputs
Port 0 also receives the code bytes during EPROM
programming and outputs the code bytes during
program verification External pullup resistors are re-
quired during program verification
Port 1
Port 1 is an 8-bit bidirectional I O port with
internal pullups The Port 1 output buffers can drive
LS TTL inputs Port 1 pins that have 1’s written to
them are pulled high by the internal pullups and in
that state can be used as inputs As inputs Port 1
pins that are externally pulled low will source current
(I
IL
on the data sheet) because of the internal pull-
ups
In addition Port 1 serves the functions of the follow-
ing special features of the 8XC51RX
Port Pin
P1 0
P1 1
Alternate Function
T2 (External Count Input to Timer
Counter 2) Clock-Out
T2EX (Timer Counter 2 Capture
Reload Trigger and Direction Control)
Port 1 receives the low-order address bytes during
EPROM programming and verifying
Port 2
Port 2 is an 8-bit bidirectional I O port with
internal pullups The Port 2 output buffers can drive
RST
Reset I O A high on this pin for two machine
cycles while the oscillator is running resets the de-
vice The port pins will be driven to their reset condi-
tion when a minimum V
IHI
voltage is applied whether
the oscillator is running or not An internal pulldown
resistor permits a power-on reset with only a capaci-
tor connected to V
CC
After a WatchDog Timer over-
flow this RST pin will drive an output high pulse at a
minimum V
OH2
for 96 x T
OSC
duration while the in-
ternal reset signal is active
ALE
Address Latch Enable output pulse for latching
the low byte of the address during accesses to ex-
4
8XC51RA RB RC
ternal memory This pin (ALE PROG) is also the
program pulse input during EPROM programming for
the 87C51RX
In normal operation ALE is emitted at a constant
rate of
the oscillator frequency and may be used
for external timing or clocking purposes Note how-
ever that one ALE pulse is skipped during each ac-
cess to external Data Memory
If desired ALE operation can be disabled by setting
bit 0 of SFR location 8EH With this bit set the pin is
weakly pulled high However the ALE disable fea-
ture will be suspended during a MOVX or MOVC in-
struction idle mode power down mode and ICE
mode The ALE disable feature will be terminated by
reset When the ALE disable feature is suspended or
terminated the ALE pin will no longer be pulled up
weakly Setting the ALE-disable bit has no affect if
the microcontroller is in external execution mode
Throughout the remainder of this data sheet ALE
will refer to the signal coming out of the ALE PROG
pin and the pin will be referred to as the ALE PROG
pin
PSEN
Program Store Enable is the read strobe to
external Program Memory
When the 8XC51RX is executing code from external
Program Memory PSEN is activated twice each
machine cycle except that two PSEN activations
are skipped during each access to external Data
Memory
EA V
PP
External Access enable EA must be
strapped to VSS in order to enable the device to
fetch code from external Program Memory locations
0000H to 0FFFFH Note however that if any of the
Lock bits are programmed EA will be internally
latched on reset
EA should be strapped to V
CC
for internal program
executions
This pin also receives the programming supply volt-
age (V
PP
) during EPROM programming
XTAL1
Input to the inverting oscillator amplifier
XTAL2
Output from the inverting oscillator amplifi-
er
272659 – 6
ured for use as an on-chip oscillator as shown in
Figure 3 Either a quartz crystal or ceramic resonator
may be used More detailed information concerning
the use of the on-chip oscillator is available in Appli-
cation Note AP-155 ‘‘Oscillators for Microcontrol-
lers’’ Order No 230659
272659 –5
C1 C2
e
30 pF
g
10 pF for Crystals
For Ceramic Resonators contact resonator manufac-
turer
Figure 3 Oscillator Connections
To drive the device from an external clock source
XTAL1 should be driven while XTAL2 floats as
shown in Figure 4 There are no requirements on the
duty cycle of the external clock signal since the in-
put to the internal clocking circuitry is through a di-
vide-by-two flip-flop but minimum and maximum
high and low times specified on the data sheet must
be observed
An external oscillator may encounter as much as a
100 pF load at XTAL1 when it starts up This is due
to interaction between the amplifier and its feedback
capacitance Once the external signal meets the V
IL
and V
IH
specifications the capacitance will not ex-
ceed 20 pF
Figure 4 External Clock Drive Configuration
IDLE MODE
The user’s software can invoke the Idle Mode When
the microcontroller is in this mode power consump-
tion is reduced The Special Function Registers and
the onboard RAM retain their values during Idle but
the processor stops executing instructions Idle
OSCILLATOR CHARACTERISTICS
XTAL1 and XTAL2 are the input and output respec-
tively of a inverting amplifier which can be config-
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