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Erostek ET-232


This document is a specification for the serial communications protocol of the ET232 Electrostimulation box by Erostek. The protocol was put together through information found around the internet.

Communicating with the ET-232 box happens via an RS-232 Connection to the Link port of the box. The link cable consists of a 3.5mm TRS (stereo audio) jack, going to some sort of computer connection, be it Female DB-9 or a RS232-to-USB converter. The pin connections are as follows:

  • 3.5mm Tip <-> RX (DB-9 Pin 2)
  • 3.5mm Ring <-> TX (DB-9 Pin 3)
  • 3.5mm Sleeve <-> Ground (DB-9 Pin 5)

Serial connections are 19200/8/N/1, or:

  • 19200 baud
  • Data Bits: 8
  • Stop Bits: 1
  • Partity: None

To use the serial link on the ET-232, the cable must be plugged in before the box is turned on, in order to complete the handshake protocol. Otherwise, the jack will register as an audio input jack. Similarly, to use the jack as audio once again, the box should be turned off and back on first, in order to reestablish audio mode.


When the box is powered on, the ET-232 will send a single byte:


Assuming this is transferred correctly, the box then listens for and responds to commands. Unlike the ET-312, the ET-232 does not use an encrypted protocol.



Commands work on a peek and poke basis, similar to the ET-312.

Commands consist:

  • ASCII characters
  • A 2-byte checksum string, meaning two ASCII uppercase characters representing one hex byte. The checksum is a sum of all the characters in the range from '0' (0x30) to 'Z' (0x90) in the string. All characters outside of this range are ignored for the purposes of the checksum. This would be output by using a "%02X" printf-style formatter, for instance.
  • A "\r" character to end the command.

Valid commands will be acknowledged with the following string:


If a command is unrecognized, or the checksum does not match, the following string will be returned:


Read Byte ("H")

Reading a byte from the ET-232 is done using the "H" command. This command consists of:

  • "H" (0x48)
  • A 8-bit address, written as 2 ASCII characters representing the hex value.
  • The checksum
  • "\r"

For instance, to read the byte at 0x80 (which gives you a checksum of 0xB0), you would send


The command will return a two digit hex value at the requested location, in ASCII

Write Byte ("I")

Writing a byte from the ET-232 is done using the "I" command. This command consists of:

  • "I" (0x49)
  • A 8-bit address, written as 2 ASCII characters representing the hex value.
  • An 8-bit value, written as 2 ASCII characters representing the hex value.
  • The checksum
  • "\r"

For instance, to write the value 0x10 to the byte at 0x80 (which gives you a checksum of 0x12), you would send


The command, if successful, will return the string "$\n"

Unknown ("J")

The usage of the "J" command is unknown. Sending "J" appears to ignore arguments and returns "FF\n"

Address Table

$08Channel A Pulse Width
$09Channel A Pulse Frequency Reciprocal
$0AChannel A Pulse Amplitude
$0BChannel A Power Compensation
$0CChannel A Pulse Enable Polarity
$0EChannel B Pulse Width
$0FChannel B Pulse Frequency Reciprocal
$10Channel B Pulse Amplitude
$11Channel B Power Compensation
$12Channel B Pulse Enable Polarity
$20-4FRAM/Program Parameters?
$88Position of Pot B
$89Position of MA Pot
$8ABattery Voltage
$8BAudio Input Level
$8CPosition of Pot A
$98Position of MA Pot (?)
$A2Mode Switch Position
$A3Mode Switch Override
$A4Analog Input Override
$D0Unknown Timer
$D1Unknown Timer
$D3Auto Power Off Timer
$D8Program Fade In Timer
$FCUnknown Timer
$FDUnknown Timer

Address Specific Notes

$08/$0E - Channel Pulse Width

Range is 00 (very low) to FF (full effect).

$09/$0F - Channel Pulse Frequency Reciprocal

Maximum range is FF (~15Hz) to 08 (~475Hz).

$0A/$10 - Channel Pulse Amplitude

Range is 00 (no output) to FF (full effect).

Whereas the pulse width is perceptually linear, this parameter has a quadratic effect on overall power, so changes are more discernible at the upper end.

$0B/$11 - Channel Power Compentation

Most programs use 20 as the standard value. Stroke uses 2B (to compensate for the monophasic pulses?). Small numeric increases produce relative large increases in perceived intensity.

$0C/$12 - Channel Pulse Enable/Polarity

Most programs use 07 as the standard value. Some switch between 07 and 06 to provide an intermittent effect. Stroke switches between 05 and 03 to produce the two different stroke "directions".

$88/$89/$8C/$98 - Pot Positions

Values range from 00 (far left) to FF (far right)

$8A - Battery Voltage

FF (maximum) to 90 (auto shutdown threshold)

$A2 - Mode Switch Position


$A3 - Mode Switch Override

  • 8X - force modeX
  • 8F - force reset

When top bit set, the requested mode is selected regardless of the position of the physical switch. Even if the switch is moved to off! If serial connection is lost for any reason in this state, then it may be necessary to remove power from the device in order to reset it.

$A4 - Analog Input Override

01disable input B
02disable input MA
04disable input Battery
08disable input Audio
10disable input A

When set, the corresponding inputs are ignored, and levels can be set in software by writing to addresses 88..8C above.