Explore the internal circuitry and functional stages of MAX232.
Package view
Inside MAX232
Charge pump · Line drivers · Line receivers
Functional block diagram. The charge-pump capacitors connect outside the IC; see Basic Circuit for their wiring.
Explore the circuit
Select a stage to see its role and connections
Charge pump
The first switched-capacitor stage doubles the 5 V supply. The second stage inverts that positive rail, giving the transmitters both polarities from one supply. C1 and C2 transfer charge; C3 and C4 store it. C5 keeps the supply stable.
Flying capacitors
C1: pins 1–3 · C2: pins 4–5
Reservoir capacitors
VS+: pin 2 · VS−: pin 6
External parts
Five 1 µF capacitors, including supply bypass
Driver rails
Approximately +10 V and −10 V are idealized values. Real rails and output swing drop under load.
Transmitter 1
Converts the local logic output into an inverted bipolar RS-232 signal.
InputT1IN · pin 11 · TTL / CMOS
OutputT1OUT · pin 14 · RS-232
This stage inverts the signal polarity.
Transmitter 2
A second independent transmit path, powered by the same internal charge pump.
InputT2IN · pin 10 · TTL / CMOS
OutputT2OUT · pin 7 · RS-232
This stage inverts the signal polarity.
Receiver 1
Accepts an RS-232 line signal and provides an inverted logic-level output for the local UART.
InputR1IN · pin 13 · RS-232
OutputR1OUT · pin 12 · TTL / CMOS
This stage inverts the signal polarity.
Receiver 2
The second receive path works independently of receiver 1. Both use the common ground reference.
InputR2IN · pin 8 · RS-232
OutputR2OUT · pin 9 · TTL / CMOS
This stage inverts the signal polarity.
Input resistance and reference details
The 400 kΩ pullups and 5 kΩ receiver loads show the internal equivalent in Maxim’s reference diagram. They are not extra parts you need to connect.
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