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RS-232 transceiver

MAX232 Basic Circuit

Build a basic MAX232 circuit with labeled pins, component values and connection guidance.

Package view

MAX232 in a circuit

5 V supply · Charge-pump capacitors · UART ↔ RS-232

A complete MAX232 interface with a microcontroller, five capacitors and a DB9 connector The chip is shown from the top with physical pins 1 to 8 on the left, and 16 to 9 on the right. VCC pin 16 uses 5 volts; pin 15 shares ground with the microcontroller and DB9 pin 5. C1 connects pins 1 and 3, C2 pins 4 and 5, C3 connects VS+ pin 2 to 5 volts, C4 connects VS− pin 6 to ground, and C5 bypasses the supply. All capacitors are 1 microfarad. Microcontroller TX goes to T1IN 11. R1OUT 12 goes to microcontroller RX. T1OUT 14 goes to DB9 pin 2, and DB9 pin 3 goes to R1IN 13. The connector is a DCE female, shown from its mating face, for a straight-through cable to a PC DTE port. Channel 2 is unused. A REAL-WORLD UART ↔ RS-232 INTERFACE Color follows the connection. Numbers identify the physical IC pins. +C1Flying capacitor +C2Flying capacitor +C3Positive reservoir +C4Negative reservoir C1+VCC VS+GND C1−T1OUT C2+R1IN C2−R1OUT VS−T1IN T2OUTT2IN R2INR2OUTMAX232TOP VIEW MICROCONTROLLER RXTXGND MCU 5 V UART logic · TX and RX are separate DB9 SERIAL CONNECTOR 543219876DCE female · mating-face viewStraight-through cable to a PC DTE port +5 V + C5 · BypassClose to pins 16 / 15 5 · GND GNDGND All GND symbols connect to the same signal ground. TX → 11 RX ← 12 14 → 2 · RXD 13 ← 3 · TXD11621531441351261171089C1–C5: 1 µF each+ marks the positive terminal. Channel 1 shown · channel 2 unused
Top-view IC pin numbers. DB9: DCE female, mating face. Gold capacitor symbols show polarity; all GND symbols share signal ground.

Connect it, step by step

Follow the component values and pin connections

Power first

Pin 16 → regulated 5 V. Pin 15 → common ground. Put a 1 µF bypass close to these pins.

Regulated +5 V
VCC · pin 16
Signal ground
GND · pin 15, MCU & DB9 pin 5
C5 · 1 µF bypass
VCC ↔ GND, close to the IC

Add the charge pump

C1: 1–3. C2: 4–5. C3: 2–VCC. C4: GND–6. All are 1 µF; the + signs show polarized-capacitor orientation.

C1 · 1 µF
Pin 1 (+) ↔ pin 3 (−)
C2 · 1 µF
Pin 4 (+) ↔ pin 5 (−)
C3 · 1 µF
Pin 2 (+) ↔ VCC (−)
C4 · 1 µF
GND (+) ↔ pin 6 (−)

Connect the local UART

TX → T1IN (11). RX ← R1OUT (12). These are the logic-side connections.

MCU TX
T1IN · pin 11
R1OUT · pin 12
MCU RX

Connect the remote interface

T1OUT (14) → DB9 pin 2. DB9 pin 3 → R1IN (13). Pin 5 → common ground. This DCE female connector uses a straight-through cable to a PC’s DTE port.

T1OUT · pin 14
DB9 pin 2 · PC receive
DB9 pin 3 · PC transmit
R1IN · pin 13
DB9 pin 5
Common signal ground

Use the second channel in the same way: T2IN (10) → T2OUT (7), and R2IN (8) → R2OUT (9).

C3 may return to VCC or ground; this guide uses VCC, matching the featured circuit. Ceramic capacitors are acceptable. Follow the datasheet for the exact part and layout.

Component view