Features
• Compatible with MCS-51
• 2K Bytes of Reprogrammable Flash Memory
– Endurance: 1,000 Write/Erase Cycles
• 2.7V to 6V Operating Range
• Fully Static Operation: 0 Hz to 24 MHz
• Two-level Program Memory Lock
• 128 x 8-bit Internal RAM
• 15 Programmable I/O Lines
• Two 16-bit Timer/Counters
• Six Interrupt Sources
• Programmable Serial UART Channel
• Direct LED Drive Outputs
• On-chip Analog Comparator
• Low-power Idle and Power-down Modes
™
Products
8-bit
Microcontroller
with 2K Bytes
Description
The AT89C2051 is a low-voltage, high-performance CMOS 8-bit microcomputer with
2K bytes of Flash programmable and erasable read only memory (PEROM). The
device is manufactured using Atmel’s high-density nonvolatile memory technology
and is compatible with the industry-standard MCS-51 instruction set. By combining a
versatile 8-bit CPU with Flash on a monolithic chip, the Atmel AT89C2051 is a powerful microcomputer which provides a highly-flexible and cost-effective solution to many
embedded control applications.
The AT89C2051 provides the following standard features: 2K bytes of Flash, 128
bytes of RAM, 15 I/O lines, two 16-bit timer/counters, a five vector two-level interrupt
architecture, a full duplex serial port, a precision analog comparator, on-chip oscillator
and clock circuitry. In addition, the AT89C2051 is designed with static logic for operation down to zero frequency and supports two software selectable power saving
modes. The Idle Mode stops the CPU while allowing the RAM, timer/counters, serial
port and interrupt system to continue functioning. The power-down mode saves the
RAM contents but freezes the oscillator disabling all other chip functions until the next
hardware reset.
Pin Configuration
PDIP/SOIC
RST/VPP
(RXD) P3.0
(TXD) P3.1
XTAL2
XTAL1
(INT0) P3.2
(INT1) P3.3
(TO) P3.4
(T1) P3.5
GND
1
2
3
4
5
6
7
8
9
10
20
19
18
17
16
15
14
13
12
11
VCC
P1.7
P1.6
P1.5
P1.4
P1.3
P1.2
P1.1 (AIN1)
P1.0 (AIN0)
P3.7
Flash
AT89C2051
Rev. 0368E–02/00
1
Block Diagram
2
AT89C2051
AT89C2051
Pin Description
VCC
Supply voltage.
GND
Ground.
Port 1
Port 1 is an 8-bit bi-irectional I/O port. Port pins P1.2 to
P1.7 provide internal pullups. P1.0 and P1.1 require external pullups. P1.0 and P1.1 also serve as the positive input
(AIN0) and the negative input (AIN1), respectively, of the
on-chip precision analog comparator. The Port 1 output
buffers can sink 20 mA and can drive LED displays directly.
When 1s are written to Port 1 pins, they can be used as
inputs. When pins P1.2 to P1.7 are used as inputs and are
externally pulled low, they will source current (I
of the internal pullups.
Port 1 also receives code data during Flash programming
and verification.
Port 3
Port 3 pins P3.0 to P3.5, P3.7 are seven bi-irectional I/O
pins with internal pullups. P3.6 is hard-wired as an input to
the output of the on-chip comparator and is not accessible
as a general purpose I/O pin. The Port 3 output buffers can
sink 20 mA. When 1s are written to Port 3 pins they are
pulled high by the internal pullups and can be used as
inputs. As inputs, Port 3 pins that are externally being
pulled low will source current (I
) because of the pullups.
IL
Port 3 also serves the functions of various special features
of the AT89C2051 as listed below:
) because
IL
Each machine cycle takes 12 oscillator or clock cycles.
XTAL1
Input to the inverting oscillator amplifier and input to the
internal clock operating circuit.
XTAL2
Output from the inverting oscillator amplifier.
Oscillator Characteristics
XTAL1 and XTAL2 are the input and output, respectively,
of an inverting amplifier which can be configured for use as
an on-chip oscillator, as shown in Figure 1. Either a quartz
crystal or ceramic resonator may be used. To drive the
device from an external clock source, XTAL2 should be left
unconnected while XTAL1 is driven as shown in Figure 2.
There are no requirements on the duty cycle of the external
clock signal, since the input to the internal clocking circuitry
is through a divide-by-two flip-flop, but minimum and maximum voltage high and low time specifications must be
observed.
Figure 1. Oscillator Connections
Port Pin Alternate Functions
P3.0 RXD (serial input port)
P3.1 TXD (serial output port)
P3.2 INT0
P3.3 INT1
P3.4 T0 (timer 0 external input)
P3.5 T1 (timer 1 external input)
(external interrupt 0)
(external interrupt 1)
Port 3 also receives some control signals for Flash programming and verification.
RST
Reset input. All I/O pins are reset to 1s as soon as RST
goes high. Holding the RST pin high for two machine
cycles while the oscillator is running resets the device.
Note: C1, C2 = 30 pF ± 10 pF for Crystals
= 40 pF ± 10 pF for Ceramic Resonators
Figure 2. External Clock Drive Configuration
3
Special Function Registers
A map of the on-chip memory area called the Special Function Register (SFR) space is shown in the table below.
Note that not all of the addresses are occupied, and unoccupied addresses may not be implemented on the chip.
Read accesses to these addresses will in general return
random data, and write accesses will have an indeterminate effect.
User software should not write 1s to these unlisted locations, since they may be used in future products to invoke
new features. In that case, the reset or inactive values of
the new bits will always be 0.
Table 1. AT89C2051 SFR Map and Reset Values
0F8H 0FFH
0F0H B
00000000
0E8H 0EFH
0E0H ACC
00000000
0D8H 0DFH
0D0H PSW
00000000
0C8H 0CFH
0F7H
0E7H
0D7H
0C0H 0C7H
0B8H IP
XXX00000
0B0H P3
11111111
0A8H IE
0XX00000
0A0H 0A7H
98H SCON
00000000
90H P1
11111111
88H TCON
00000000
80H SP
SBUF
XXXXXXXX
TMOD
00000000
00000111
TL0
00000000
DPL
00000000
TL1
00000000
DPH
00000000
TH0
00000000
TH1
00000000
PCON
0XXX0000
0BFH
0B7H
0AFH
9FH
97H
8FH
87H
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AT89C2051
AT89C2051
Restrictions on Certain Instructions
The AT89C2051 and is an economical and cost-effective
member of Atmel’s growing family of microcontrollers. It
contains 2K bytes of flash program memory. It is fully compatible with the MCS-51 architecture, and can be
programmed using the MCS-51 instruction set. However,
there are a few considerations one must keep in mind
when utilizing certain instructions to program this device.
All the instructions related to jumping or branching should
be restricted such that the destination address falls within
the physical program memory space of the device, which is
2K for the AT89C2051. This should be the responsibility of
the software programmer. For example, LJMP 7E0H
would be a valid instruction for the AT89C2051 (with 2K of
memory), whereas LJMP 900H would not.
1. Branching instructions:
LCALL, LJMP, ACALL, AJMP, SJMP, JMP @A+DPTR
These unconditional branching instructions will execute
correctly as long as the programmer keeps in mind that the
destination branching address must fall within the physical
boundaries of the program memory size (locations 00H to
7FFH for the 89C2051). Violating the physical space limits
may cause unknown program behavior.
CJNE [...], DJNZ [...], JB, JNB, JC, JNC, JBC, JZ, JNZ With
these conditional branching instructions the same rule
above applies. Again, violating the memory boundaries
may cause erratic execution.
For applications involving interrupts the normal interrupt
service routine address locations of the 80C51 family architecture have been preserved.
2. MOVX-related instructions, Data Memory:
The AT89C2051 contains 128 bytes of internal data memory. Thus, in the AT89C2051 the stack depth is limited to
128 bytes, the amount of available RAM. External DATA
memory access is not supported in this device, nor is external PROGRAM memory execution. Therefore, no MOVX
[...] instructions should be included in the program.
A typical 80C51 assembler will still assemble instructions,
even if they are written in violation of the restrictions mentioned above. It is the responsibility of the controller user to
know the physical features and limitations of the device
being used and adjust the instructions used
correspondingly.
Program Memory Lock Bits
On the chip are two lock bits which can be left unprogrammed (U) or can be programmed (P) to obtain the
additional features listed in the table below:
Lock Bit Protection Modes
Program Lock Bits
LB1 LB2 Protection Type
1 U U No program lock features.
2 P U Further programming of the Flash
is disabled.
3 P P Same as mode 2, also verify is
disabled.
Note: 1. The Lock Bits can only be erased with the Chip Erase
operation.
(1)
Idle Mode
In idle mode, the CPU puts itself to sleep while all the onchip peripherals remain active. The mode is invoked by
software. The content of the on-chip RAM and all the special functions registers remain unchanged during this
mode. The idle mode can be terminated by any enabled
interrupt or by a hardware reset.
P1.0 and P1.1 should be set to “0” if no external pullups are
used, or set to “1” if external pullups are used.
It should be noted that when idle is terminated by a hardware reset, the device normally resumes program
execution, from where it left off, up to two machine cycles
before the internal reset algorithm takes control. On-chip
hardware inhibits access to internal RAM in this event, but
access to the port pins is not inhibited. To eliminate the
possibility of an unexpected write to a port pin when Idle is
terminated by reset, the instruction following the one that
invokes Idle should not be one that writes to a port pin or to
external memory.
Power-down Mode
In the power down mode the oscillator is stopped, and the
instruction that invokes power down is the last instruction
executed. The on-chip RAM and Special Function Registers retain their values until the power down mode is
terminated. The only exit from power down is a hardware
reset. Reset redefines the SFRs but does not change the
on-chip RAM. The reset should not be activated before V
is restored to its normal operating level and must be held
active long enough to allow the oscillator to restart and
stabilize.
P1.0 and P1.1 should be set to “0” if no external pullups are
used, or set to “1” if external pullups are used.
CC
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