ATtiny2313 — 20-Pin 8-Bit AVR Microcontroller with Hardware USART (DIP-20)

Overview

The ATtiny2313 (ATtiny2313A) is a classic 20-pin 8-bit AVR RISC microcontroller manufactured by Microchip Technology (originally Atmel) in a DIP-20 through-hole and SOIC-20 surface-mount package. Serving as the modernized replacement for the vintage AT90S2313, it provides a generous 18 GPIO lines and a full hardware USART in a narrow 20-pin format.

Operating from $1.8\text{V}$ to $5.5\text{V}$ DC at up to $20\text{ MHz}$ , the ATtiny2313 features $2\text{ KB}$ Flash, $128\text{ Bytes}$ SRAM, $128\text{ Bytes}$ EEPROM, an 8-bit timer, a 16-bit timer with 4 PWM outputs, an analog comparator, and a Universal Serial Interface (USI supporting SPI and I2C). Because of its built-in hardware UART transceiver, it was prominently featured across 2000s DIY electronics magazines (Nuts & Volts, Elektor, Circuit Cellar) for dedicated serial display controllers, LED matrix drivers, frequency counters, and MIDI processors.

Quick reference


CPU Core	8-bit AVR RISC Architecture
Package	20-pin DIP (DIP-20 / PDIP-20) / 20-pin SOIC / 20-pin QFN
Max Clock Frequency	$20\text{ MHz}$ ( $8\text{ MHz}$ calibrated internal RC)
Flash Memory	$2048\text{ Bytes}$ ( $2\text{ KB}$ ) non-volatile storage
SRAM	$128\text{ Bytes}$ internal RAM
EEPROM	$128\text{ Bytes}$ non-volatile data storage
Supply Voltage Range	$1.8\text{ V}$ to $5.5\text{ V}$ DC ( $2.7\text{V} \dots 5.5\text{V}$ for $10\text{MHz}$ , $4.5\text{V} \dots 5.5\text{V}$ for $20\text{MHz}$ )
GPIO Count	18 Programmable I/O lines
Hardware USART	Full duplex hardware UART (Pins `PD0/RXD`, `PD1/TXD`)
PWM Channels	4 PWM channels (`OC0A`, `OC0B`, `OC1A`, `OC1B`)
Serial Bus	USI (Universal Serial Interface for SPI / I2C)

Pinout (DIP-20 Package)

text

                            ┌───┴───┐
      (Active-Low/dW) PA2 1│ 1   20│ VCC (+1.8V to +5.5V)
             (RXD) PD0 2│       │19 PB7 (UCSK / SCL / SCK)
             (TXD) PD1 3│       │18 PB6 (DO / MISO)
           (XTAL2) PA1 4│ATtiny │17 PB5 (DI / SDA / MOSI)
           (XTAL1) PA0 5│ 2313  │16 PB4 (OC1B / PCINT4)
          (CKOUT) PD2 6│DIP-20 │15 PB3 (OC1A / PCINT3)
            (INT1) PD3 7│       │14 PB2 (OC0A / PCINT2)
              (T0) PD4 8│       │13 PB1 (AIN1 / PCINT1)
         (OC0B/T1) PD5 9│       │12 PB0 (AIN0 / PCINT0)
                   GND 10│      │11 PD6 (ICP)
                            └───────┘

Pin	Name	Type	Description
1	`PA2 / RESET`	GPIO / Reset	Active-LOW Reset / `dW` (debugWIRE) / `PCINT9`
2	`PD0 / RXD`	GPIO / Digital	Hardware UART Receive `RXD` / `PCINT11`
3	`PD1 / TXD`	GPIO / Digital	Hardware UART Transmit `TXD` / `PCINT12`
4, 5	`PA1`, `PA0`	GPIO / Clock	Crystal Oscillator pins (`XTAL2`, `XTAL1`)
6	`PD2`	GPIO / Digital	`INT0` / `CKOUT` / `XCK`
7, 8, 9	`PD3`-`PD5`	GPIO / Digital	`INT1` / Timer0 `T0` / Timer1 `T1` / PWM `OC0B`
10	`GND`	Power	Common Ground reference ( $0\text{ V}$ )
11	`PD6`	GPIO / Digital	Timer1 Input Capture Pin (`ICP`)
12, 13	`PB0`, `PB1`	GPIO / Analog	Analog Comparator Inputs (`AIN0`, `AIN1`)
14, 15, 16	`PB2`-`PB4`	GPIO / Digital	PWM Channels `OC0A`, `OC1A`, `OC1B`
17	`PB5 / MOSI`	GPIO / SPI	`MOSI` (ISP) / USI Data Input `DI` / I2C `SDA`
18	`PB6 / MISO`	GPIO / SPI	`MISO` (ISP) / USI Data Output `DO`
19	`PB7 / SCK`	GPIO / SPI	`SCK` (ISP) / USI Clock `UCSK` / I2C `SCL`
20	`VCC`	Power	Supply Voltage ( $+1.8\text{ V}$ to $+5.5\text{ V}$ DC)

Minimal Serial Communications Hookup

text

   FTDI USB-to-UART Adapter
   ┌────────────────────────────────┐
   │ 5V / 3.3V ─────────────────────┼─────────┬──────────────► [Pin 20: VCC]
   │                                │         │                     ATtiny2313
   │                                │   [ 100nF Cap ]               DIP-20
   │                                │         │
   │ GND ───────────────────────────┼─────────┼──────────────► [Pin 10: GND]
   │ TXD ───────────────────────────┼─────────┼──────────────► [Pin 2: PD0 / RXD]
   │ RXD ───────────────────────────┼─────────┴──────────────► [Pin 3: PD1 / TXD]
   └────────────────────────────────┘

Common mistakes

Lack of built-in ADC: Unlike the ATtiny85 or ATmega328P, the ATtiny2313 has no analog-to-digital converter (ADC). It only possesses an Analog Comparator (on pins PB0/PB1). If multi-channel ADC reading is required, select the ATtiny84 or ATmega328P.
RAM constraints with serial buffering: The ATtiny2313 has only $128\text{ Bytes}$ of RAM. Standard Arduino HardwareSerial circular buffers take $64\text{ Bytes}$ each ( $128\text{ Bytes}$ total for RX+TX), consuming 100% of RAM. When using the ATTinyCore Arduino board package, configure the minimal serial buffer option ( $16\text{ Bytes}$ or $8\text{ Bytes}$ ) in the tools menu.

Notes

Pin-Compatible Drop-In Upgrade: ATtiny4313 doubles the Flash to $4\text{ KB}$ and RAM to $256\text{ Bytes}$ .
Arduino Core: Fully supported by Spence Konde's open-source ATTinyCore board package.