AT89C4051-12PU from Microchip Tech, in a PDIP-20. Pinout and pin descriptions extracted from the manufacturer datasheet (extract_pins, cross-checked by a second model); symbol, footprint, and 3D from KiCad-official CAD.

Pinout

Pin	Name	Type	Function
1	RST/VPP	input	Reset input: holding RST high for two machine cycles while the oscillator runs resets the device, and it is raised to 12V to enable Flash programming.
2	P3.0 (RXD)	bidirectional	Port 3 bidirectional I/O pin with internal pullup that serves as the serial input port RXD.
3	P3.1 (TXD)	bidirectional	Port 3 bidirectional I/O pin with internal pullup that serves as the serial output port TXD, and is pulled low to indicate BUSY during programming.
4	XTAL2	output	Output from the inverting oscillator amplifier, left unconnected when XTAL1 is driven by an external clock.
5	XTAL1	input	Input to the inverting oscillator amplifier and to the internal clock operating circuit.
6	P3.2 (INT0)	bidirectional	Port 3 bidirectional I/O pin with internal pullup that serves as external interrupt 0 and is pulsed to program a byte during Flash programming.
7	P3.3 (INT1)	bidirectional	Port 3 bidirectional I/O pin with internal pullup that serves as external interrupt 1 and is used for programming control.
8	P3.4 (T0)	bidirectional	Port 3 bidirectional I/O pin with internal pullup that serves as the external input to timer 0 and is used for programming control.
9	P3.5 (T1)	bidirectional	Port 3 bidirectional I/O pin with internal pullup that serves as the external input to timer 1 and is used for programming control.
10	GND	power_in	Ground reference for the device.
11	P3.7	bidirectional	Port 3 bidirectional I/O pin with internal pullup that is also used for Flash programming and verification control.
12	P1.0 (AIN0)	bidirectional	Port 1 bidirectional I/O pin that requires an external pullup, sinks up to 20 mA, and serves as the positive input of the on-chip analog comparator.
13	P1.1 (AIN1)	bidirectional	Port 1 bidirectional I/O pin that requires an external pullup, sinks up to 20 mA, and serves as the negative input of the on-chip analog comparator.
14	P1.2	bidirectional	Port 1 bidirectional I/O pin with internal pullup whose output buffer can sink 20 mA and drive LED displays directly.
15	P1.3	bidirectional	Port 1 bidirectional I/O pin with internal pullup whose output buffer can sink 20 mA and drive LED displays directly.
16	P1.4	bidirectional	Port 1 bidirectional I/O pin with internal pullup whose output buffer can sink 20 mA and drive LED displays directly.
17	P1.5	bidirectional	Port 1 bidirectional I/O pin with internal pullup whose output buffer can sink 20 mA and drive LED displays directly.
18	P1.6	bidirectional	Port 1 bidirectional I/O pin with internal pullup whose output buffer can sink 20 mA and drive LED displays directly.
19	P1.7	bidirectional	Port 1 bidirectional I/O pin with internal pullup whose output buffer can sink 20 mA and drive LED displays directly.
20	VCC	power_in	Supply voltage, specified for operation from 2.7V to 6.0V for the AT89C4051-12PU.

Key specifications

Parameter	Value
Manufacturer	Microchip Tech
Package	PDIP-20
Category	Embedded Processors & Controllers
Pins	20

Electrical characteristics

Limits as printed in the datasheet (page.json metadata.characteristics carries them as data).

Parameter	Symbol	Min	Max	Unit	Conditions	Page
Output Low-voltage (Ports 1, 3)	VOL		0.5	V	IOL = 10 mA, VCC = 2.7V	12
Output High-voltage (Ports 1, 3)	VOH	2.4		V	IOH = -80 µA, VCC = 5V ± 10%	12
Input Low-voltage	VIL	-0.5		V		12
Logical 0 Input Current (Ports 1, 3)	IIL		-50	µA	VIN = 0.45V	12
Logical 1 to 0 Transition Current (Ports 1, 3)	ITL		-750	µA	VIN = 2V, VCC = 5V ± 10%	12
Input Leakage Current (Port P1.0, P1.1)	ILI	-10	10	µA	0 < VIN < VCC	12
Comparator Input Offset Voltage	VOS		20	mV	VCC = 5V	12
Comparator Input Common Mode Voltage	VCM	0		V		12
Reset Pulldown Resistor	RRST	50	300	KΩ		12
Pin Capacitance	CIO		10	pF	Test Freq. = 1 MHz, TA = 25°C	12
Power Supply Current, Active Mode	ICC		15	mA	Active Mode, 12 MHz, VCC = 6V	12
Power Supply Current, Active Mode	ICC		5.5	mA	Active Mode, 12 MHz, VCC = 3V	12
Power Supply Current, Idle Mode	ICC		5	mA	Idle Mode, 12 MHz, VCC = 6V; P1.0 & P1.1 = 0V or VCC	12
Power Supply Current, Idle Mode	ICC		1	mA	Idle Mode, 12 MHz, VCC = 3V; P1.0 & P1.1 = 0V or VCC	12
Power Supply Current, Power-down Mode	ICC		20	µA	VCC = 6V, P1.0 & P1.1 = 0V or VCC	12
Power Supply Current, Power-down Mode	ICC		5	µA	VCC = 3V, P1.0 & P1.1 = 0V or VCC	12
Oscillator Frequency	1/tCLCL	0	12	MHz	VCC = 2.7V to 6.0V	13
Clock Period	tCLCL	83.3		ns	VCC = 2.7V to 6.0V	13
High Time	tCHCX	30		ns	VCC = 2.7V to 6.0V	13
Low Time	tCLCX	30		ns	VCC = 2.7V to 6.0V	13
Rise Time	tCLCH		20	ns	VCC = 2.7V to 6.0V	13
Fall Time	tCHCL		20	ns	VCC = 2.7V to 6.0V	13
Serial Port Clock Cycle Time	tXLXL	1		µs	VCC = 5.0V ± 20%; Load Capacitance = 80 pF; 12 MHz Osc	14
Output Data Setup to Clock Rising Edge	tQVXH	700		ns	VCC = 5.0V ± 20%; Load Capacitance = 80 pF; 12 MHz Osc	14
Output Data Hold after Clock Rising Edge	tXHQX	50		ns	VCC = 5.0V ± 20%; Load Capacitance = 80 pF; 12 MHz Osc	14
Input Data Hold after Clock Rising Edge	tXHDX	0		ns	VCC = 5.0V ± 20%; Load Capacitance = 80 pF; 12 MHz Osc	14
Clock Rising Edge to Input Data Valid	tXHDV	700		ns	VCC = 5.0V ± 20%; Load Capacitance = 80 pF; 12 MHz Osc	14
Programming Enable Voltage	VPP	11.5	12.5	V	TA = 20°C to 30°C, VCC = 5.0 ± 10%	11
Programming Enable Current	IPP		250	µA	TA = 20°C to 30°C, VCC = 5.0 ± 10%	11
Data Setup to PROG Low	tDVGL	1		µs	TA = 20°C to 30°C, VCC = 5.0 ± 10%	11
Data Hold after PROG	tGHDX	1		µs	TA = 20°C to 30°C, VCC = 5.0 ± 10%	11
P3.4 (ENABLE) High to VPP	tEHSH	1		µs	TA = 20°C to 30°C, VCC = 5.0 ± 10%	11
VPP Setup to PROG Low	tSHGL	10		µs	TA = 20°C to 30°C, VCC = 5.0 ± 10%	11
VPP Hold after PROG	tGHSL	10		µs	TA = 20°C to 30°C, VCC = 5.0 ± 10%	11
PROG Width	tGLGH	1	110	µs	TA = 20°C to 30°C, VCC = 5.0 ± 10%	11
ENABLE Low to Data Valid	tELQV		1	µs	TA = 20°C to 30°C, VCC = 5.0 ± 10%	11
Data Float after ENABLE	tEHQZ	0	1	µs	TA = 20°C to 30°C, VCC = 5.0 ± 10%	11
PROG High to BUSY Low	tGHBL		50	ns	TA = 20°C to 30°C, VCC = 5.0 ± 10%	11
Byte Write Cycle Time	tWC		2	ms	TA = 20°C to 30°C, VCC = 5.0 ± 10%	11
RDY/BSY to Increment Clock Delay	tBHIH	1		µs	TA = 20°C to 30°C, VCC = 5.0 ± 10%	11
Increment Clock High	tIHIL	200		ns	TA = 20°C to 30°C, VCC = 5.0 ± 10%	11
Operating Temperature		-55	125	°C		12
Storage Temperature		-65	150	°C		12
Voltage on Any Pin with Respect to Ground		-1	7	V		12
Maximum Operating Voltage			6.6	V		12
DC Output Current			25	mA		12
Supply Voltage (AT89C4051-12PU)	VCC	2.7	6	V	12 MHz speed grade	16
Operating Temperature (Industrial)		-40	85	°C	Industrial operation range	16
Minimum VCC for Power-down	VCC	2		V	Note 2	12
Maximum IOL per Port Pin	IOL		20	mA	Note 1: steady state conditions	12
Maximum Total IOL for All Output Pins	IOL		80	mA	Note 1: steady state conditions	12
Brown-out Detection Threshold Tolerance (nominal 2.1 V)		-10	10	%		7

CAD (KiCad official)

Symbol: AT89C4051-12PU
Footprint: Package_DIP:DIP-20_W7.62mm
3D model: PDIP-20 (KiCad packages3D, STEP)
3D model files: at89c4051-12pu-etched.step / at89c4051-12pu-etched.glb carry the MPN laser-etched on the die in a toggleable Adom.LaserEtch group (Fusion-ready); at89c4051-12pu.step / at89c4051-12pu.glb are the bare package body.

Provenance

Data extracted from the manufacturer datasheet, not a distributor listing:

Datasheet: Microchip Tech datasheet (19 pp, sha256 7dd0a76556785ab0, retrieved 2026-11-11, tier: manufacturer)
Extractor: parts-factory 2.0.0 / extract_pins 0.3, primary claude-haiku-5-5 (text), consensus claude-sonnet-5-5 (agreed), guards: pin_guards 0.1: passed. Pins are checked against the footprint pad set and their cited datasheet pages before publish.
CAD: KiCad official libraries (CC-BY-SA 4.0).

Datasheet PDF

AT89C4051-12PU

Verified AT89C4051-12PU

Verification log 2 records

3D Model

Symbol & Footprint

Schematic Symbol

PCB Footprint

Datasheet

README