Pin Configuration

PDIP/SOIC

RST/VPP

(RXD) P3.0

(TXD) P3.1

XTAL2

XTAL1

(INT0) P3.2

(INT1) P3.3

(T0) P3.4

(T1) P3.5

GND

VCC

P1.7

P1.6

P1.5

P1.4

P1.3

P1.2

P1.1 (AIN1)

P1.0 (AIN0)

P3.7

Features

Compatible with MCS-51

Products

1K 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

64 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

Description

The AT89C1051U is a low-voltage, high-performance CMOS 8-bit microcomputer with
1K bytes of Flash programmable and erasable read only memory. It has the same
functionality and operation as the AT89C1051 with the addition of a UART program-
mable serial port. 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
AT89C1051U is a powerful microcomputer which provides a highly flexible and cost
effective solution to many embedded control applications.

The AT89C1051U provides the following standard features: 1K bytes of Flash, 64
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 AT89C1051U is designed with static logic for oper-
ation 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.

Rev. 1045A05/98

8-Bit
Microcontroller
with 1K Bytes
Flash

AT89C1051U
Preliminary

AT89C1051U

Pin Description

Supply voltage.

GND
Ground.

Port 1
Port 1 is an 8-bit bidirectional I/O port. Port pins P1.2 to
P1.7 provide internal pullups. P1.0 and P1.1 require exter-
nal 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

) because

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 bidirectional 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.

Port 3 also serves the functions of various special features
of the AT89C1051U as listed below:

Port 3 also receives some control signals for Flash pro-
gramming 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.

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 maxi-
mum voltage high and low time specifications must be
observed.

Figure 1. Oscillator Connections

Note:

C1, C2= 30 pF

10 pF for Crystals

= 40 pF

10 pF for Ceramic Resonators

Figure 2. External Clock Drive Configuration

Port Pin

Alternate Functions

P3.0

RXD (serial input port)

P3.1

TXD (serial output port)

P3.2

INT0 (external interrupt 0)

P3.3

INT1 (external interrupt 1)

P3.4

T0 (timer 0 external input)

P3.5

T1 (timer 1 external input)

AT89C1051U

Special Function Registers

A map of the on-chip memory area called the Special Func-
tion Register (SFR) space is shown in the table below.

Note that not all of the addresses are occupied, and unoc-
cupied 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 indetermi-
nate effect.

User software should not write 1s to these unlisted loca-
tions, 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. AT89C1051U SFR Map and Reset Values

0F8H

0FFH

0F0H

00000000

0F7H

0E8H

0EFH

0E0H

ACC

00000000

0E7H

0D8H

0DFH

0D0H

PSW

00000000

0D7H

0C8H

0CFH

0C0H

0C7H

0B8H

XXX00000

0BFH

0B0H

11111111

0B7H

0A8H

0XX00000

0AFH

0A0H

0A7H

98H

SCON

00000000

SBUF

XXXXXXXX

9FH

90H

11111111

97H

88H

TCON

00000000

TMOD

00000000

TL0

00000000

TL1

00000000

TH0

00000000

TH1

00000000

8FH

80H

00000111

DPL

00000000

DPH

00000000

PCON

0XXX0000

87H

AT89C1051U

Restrictions on Certain Instructions

The AT89C1051U and is an economical and cost-effective
member of Atmel's growing family of microcontrollers. It
contains 1K bytes of flash program memory. It is fully com-
patible with the MCS-51 architecture, and can be pro-
grammed using the MCS-51 instruction set. However, there
are a few considerations one must keep in mind when uti-
lizing 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
1K for the AT89C1051U. This should be the responsibility
of the software programmer. For example, LJMP 3FEH
would be a valid instruction for the AT89C1051U (with 1K
of memory), whereas LJMP 410H 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
3FFH for the 89C1051U). Violating the physical space lim-
its 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 archi-
tecture have been preserved.

2. MOVX-related instructions, Data Memory:
The AT89C1051U contains 64 bytes of internal data mem-
ory. Thus, in the AT89C1051U the stack depth is limited to
64 bytes, the amount of available RAM. External DATA
memory access is not supported in this device, nor is exter-
nal 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 men-
tioned 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 correspond-
ingly.

Programmable Serial UART Channel

(1)

The AT89C1051U offers a programmable serial port which
is compatible with the serial ports on other AT89 series
flash MCU products. A detailed description of the serial port
operation can be found in the Hardware Description section
of the Atmel AT89 series flash MCU data book.

Note:

This feature is not available on the AT89C1051.

Program Memory Lock Bits

On the chip are two lock bits which can be left unpro-
grammed (U) or can be programmed (P) to obtain the addi-
tional features listed in the table below:

Note:

1. The Lock Bits can only be erased with the Chip Erase

operation.

Idle Mode

In idle mode, the CPU puts itself to sleep while all the on-
chip peripherals remain active. The mode is invoked by
software. The content of the on-chip RAM and all the spe-
cial 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 hard-
ware reset, the device normally resumes program execu-
tion, 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 Regis-
ters retain their values until the power down mode is termi-
nated. 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

restored to its normal operating level and must be held
active long enough to allow the oscillator to restart and sta-
bilize.

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.

Lock Bit Protection Modes

(1)

Program Lock Bits

LB1

LB2

Protection Type

No program lock features.

Further programming of the Flash
is disabled.

Same as mode 2, also verify is
disabled.

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