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You can recreate the basic, hex-keypad-and-display UT-88 experience with a Z80 RetroShield, Arduino Mega 2560, LCD, and keypad. This is a modern Arduino-based remake, not a faithful reproduction of the original UT-88 hardware: the original was based on the Intel 8080, while this project substitutes a Z80 and uses the Mega to handle supporting functions.
What this UT-88 remake includes
The project by Evgeny Adamenkov, published on Hackster.io in 2024, recreates a basic monitor-driven computer using assembled modules rather than the original machine’s boards and expansion hardware. Its interface centers on a six-digit hexadecimal display and keypad for entering monitor commands and code.
The documented parts list is:
- RetroShield Z80 for Arduino Mega: connects the Z80 to the Mega.
- Arduino Mega 2560: runs the Arduino sketch and provides the controller interface. Adamenkov selected it for its pin count and 5 V operation in this particular design; that reasoning should not be generalized to other boards or clones.
- DFRobot Gravity 1602 LCD keypad shield: the project’s listed LCD shield. It is separate from the 4×4 keypad used to enter hexadecimal values.
- 4×4 keypad: connects to sockets A8–A15 on the Mega.
- 10 cm male-to-female 8-wire cable: joins components; check the connector pitch and layout against the hardware you have.
Adamenkov’s parts list and build instructions are in the Hackster UT-88 project. They do not establish current product availability or compatibility across every board revision.
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Follow the project’s specified order: upload the Mega sketch before attaching the RetroShield. The directions below reflect the author’s instructions; they are not independent test results.
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- ATmega2560 Microcontroller: Powered by the ATmega2560, a 8-bit microcontroller running at 16 MHz with 256KB of flash memory, 8KB SRAM, and 4KB EEPROM, providing ample storage and processing power for complex and memory-intensive applications.
- 54 Digital I/O Pins & 16 Analog Inputs: Offers an expansive I/O capacity with 54 digital pins (15 of which can be used as PWM outputs), 16 analog inputs (10-bit resolution), and 4 hardware UARTs, making it ideal for large-scale projects involving multiple sensors, motors, and communication modules
- USB Connectivity for Programming: The built-in USB interface makes programming and communication straightforward through the Arduino IDE, allowing for easy sketch uploading and serial communication with external devices
- Enhanced Project Flexibility: With its large number of I/O pins, multiple serial ports, and increased memory, the Arduino Mega is perfect for complex applications such as robotics, 3D printers, home automation, and IoT systems
- Full Compatibility with Arduino IDE: Seamlessly integrates with the Arduino IDE, providing access to a vast collection of libraries, example projects, and a global community, enabling rapid development and prototyping for advanced makers and engineers
- Install the Arduino IDE and open the project’s
mega.inosketch. - Connect the Arduino Mega 2560 to the computer by USB, select the Mega board and its port in the IDE, then upload the sketch.
- Disconnect the Mega from USB and connect the RetroShield Z80 to it.
- Connect the LCD shield, the 4×4 keypad to A8–A15, and the components with the 8-wire cable according to their connector layout.
- Reconnect power and allow for startup. The author says it can take about five seconds; adjust LCD brightness if the display is difficult to read.
The author identifies 11 near the top middle of the LCD as the ready indication. If it does not appear, check the sketch upload and assembly, then allow the stated startup time and verify display brightness before proceeding.
Memory, clock, and EEPROM storage
The following figures describe Adamenkov’s implementation, not the original UT-88 hardware or independently measured results:
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- MORE I/O FOR COMPLEX PROJECTS: Use 54 digital I/O pins with 15 PWM outputs, 16 analog inputs and expanded headers for robotics, automation, multi-sensor systems, CNC experiments and other projects that need more connections
- ATMEGA2560 MEMORY FOR LARGER SKETCHES: Run at 5 V and 16 MHz with 256 KB flash, 8 KB SRAM and 4 KB EEPROM, providing extra program space and working memory for larger control, sensing and data-handling tasks
- FOUR HARDWARE UARTS FOR MULTI-DEVICE BUILDS: Connect serial devices such as displays, GPS modules or motor controllers without sharing one port, while I2C, SPI, external interrupts and ICSP support additional expansion
- ATMEGA16U2 USB INTERFACE: Use the included USB-A to USB-B data cable for sketch uploads and serial monitoring, with the ATmega16U2 handling USB-to-serial communication between the board and a connected computer
- USB OR EXTERNAL POWER: Power the board by USB or a suitable regulated DC source through the barrel jack, and use proper drivers or separate supplies for motors and other high-current loads; includes 1 MEGA 2560 R3 board and 1 USB cable
| Component or behavior | Project-reported configuration |
|---|---|
| Z80 clock | About 0.5–0.6 MHz average, without a consistent clock. Adamenkov says, “I don’t use a timer to clock the Z80 at all,” describing an approach that toggles the clock and transfers bytes. |
| Monitor ROM | 4 KB at 0000–0FFF, containing the monitor and helper routines. |
| Default RAM | 1 KB at C000–C3FF. |
| Maximum usable RAM described | About 7 KB when the sketch uses the Mega 2560’s 8 KB SRAM. |
| Persistent user-code storage | 4 KB EEPROM divided into four sections, called “tapes” by the project. |
The LCD shows six hexadecimal digits in two groups. The keypad supplies hexadecimal keys 0–F and control functions. Physical EEPROM-backed tape buttons replace the cassette commands for storing and loading user programs.
Use the monitor directives
The project describes these monitor directives and their functions:
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- Completely compatible with original Arduino Mega2560 R3
- 1000mA current ability, the same as official board, not like some other version which uses AMS1117 that can only provide 150mA current.
- With Atmega16U2 chip as the USB to Serial converter, the same as official version
- 5V working voltage(On board 5V and 3V3 Voltage Regulator).
- Input Voltage:7-12V
| Directive | Function |
|---|---|
0 |
Write RAM beginning at a specified address. |
1 |
Write RAM beginning at C000. |
2 |
Read RAM beginning at C000. |
3 |
Run the indicator (LCD) test. |
4 |
Run the RAM test. |
5 |
Read from a specified address. |
6 |
Start execution at C000. |
7 |
Start execution at a specified address. |
8 |
Calculate a checksum for a range. |
9 and A |
Original monitor convention for tape commands; the author says not to use these in this remake. |
B |
Show time. |
C |
Set time at C3FD. |
To check the display, run directive 3; for memory, run directive 4. The author says the default RAM test should reach C400, the first address beyond the described C000–C3FF RAM range.
Select, save, and load EEPROM tapes
- Left: select a tape section.
- Up: copy RAM to the selected tape.
- Down: load the selected tape into RAM.
- Right: reset the UT-88.
Use Up and Down for this remake’s EEPROM storage instead of monitor directives 9 and A.
Rank #4
- MORE I/O FOR COMPLEX PROJECTS: Use 54 digital I/O pins with 15 PWM outputs, 16 analog inputs and expanded headers for robotics, automation, multi-sensor systems, CNC experiments and other projects that need more connections
- ATMEGA2560 MEMORY FOR LARGER SKETCHES: Run at 5 V and 16 MHz with 256 KB flash, 8 KB SRAM and 4 KB EEPROM, providing extra program space and working memory for larger control, sensing and data-handling tasks
- FOUR HARDWARE UARTS FOR MULTI-DEVICE BUILDS: Connect serial devices such as displays, GPS modules or motor controllers without sharing one port, while I2C, SPI, external interrupts and ICSP support additional expansion
- ATMEGA16U2 USB INTERFACE: Use the included USB-A to USB-B data cable for sketch uploads and serial monitoring, with the ATmega16U2 handling USB-to-serial communication between the board and a connected computer
- USB OR EXTERNAL POWER: Power the board by USB or a suitable regulated DC source through the barrel jack, and use proper drivers or separate supplies for motors and other high-current loads; includes 1 MEGA 2560 R3 board and 1 USB cable
Programming notes for the project’s monitor environment
Adamenkov lists the following addresses and routines for programs running in this implementation:
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9002,9001, and9000control the three displayed byte indicators. RST 2(D7) enters a byte from the keypad into A.IN A0(DB A0) orRST 4(E7) polls the keyboard.RST 3(DF) delays one second.RST 5(EF) displays HL and A.RST 6(F8) enters two bytes in DE.RST 0(C8) ends a program.
How this differs from the historical UT-88
The UT-88 appeared in Soviet DIY-computer magazine material in 1989, according to the UT-88 repository and emulator documentation. That account describes a staged system: a basic calculator-like machine with a six-digit display and hexadecimal keyboard, followed by a calculator add-on, a video module with a 55-key keyboard and 64×28-character display, and later memory and quasi-disk expansions.
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- 35+ Guided Electronics Projects: Progress from LEDs and buttons to RFID access, real-time clocks, motion and distance sensing, environmental monitoring, motor control and interactive displays for STEM learning, coding clubs and maker projects
- More I/O and Memory for Larger Builds: The MEGA 2560 R3 provides 54 digital I/O pins, including 15 PWM outputs, 16 analog inputs, 4 hardware serial ports and 256 KB flash for projects that combine more sensors, controls and displays
- 200+ Components for Prototyping: Includes LCD1602, RC522 RFID, RTC, DHT11, HC-SR501 PIR, ultrasonic and water-level sensors, GY-521, MAX7219, keypad, joystick, rotary encoder, relay, SG90 servo, stepper motor, DC motor, breadboard and more
- Learn, Modify and Create: Follow 35+ guided lessons with example code, then adjust sensor thresholds, timing, display text, motor behavior and control logic to turn structured exercises into access systems, monitors, alarms and interactive projects
- Organized for Repeatable Learning: Pre-soldered modules, a solderless breadboard, storage case and small-parts box reduce setup time and keep sensors, LEDs, ICs, wires and other components easy to find between projects
A Russian-language builder account, “ПК ‘Микроша’ (UT-88)”, discusses a different expanded implementation with video output, keyboard, and 64 KB dynamic RAM. It is a builder’s perspective rather than an official specification. Together, these accounts show why the Mega-based project is best understood as a minimal modern adaptation: it offers monitor-and-keypad interaction, while the historically staged system could grow into a computer with video and expanded memory.
The choice depends on what you want to recreate. The module-based project reduces the need to assemble original discrete hardware and provides EEPROM-backed program storage through the Mega. A historically oriented build involves more hardware and a different memory, display, keyboard, and storage arrangement. The available sources do not establish a part-by-part cost or a direct performance comparison.
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