Serial Tap Pro

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Serial Tap Pro is a high-performance hardware sniffer for RS232, RS485, and TTL-level UART communications, designed to meet the demands of advanced serial diagnostics. Serial Tap Pro taps into both data and control lines and streams captured traffic to IO Ninja software in real time. In addition to all the great features of the original Serial Tap, such as RS232 line jumpers, convenient quick-release terminal block, and DB9 wedge-monitoring, the Serial Tap Pro supports 2Mbps+ baud rates, features electrically isolated serial interfaces, and allows users not only to monitor but also to drive serial lines (injection). It supports 9-bit data, and delivers microsecond-precision hardware timestamps for each byte, ensuring accurate timing analysis. Featuring guaranteed byte-perfect sequencing, the Serial Tap Pro is the ultimate tool for engineers, developers and QA testers who require reliable, high-fidelity serial communication analysis on Windows, MacOS or Linux.

Board

Terminal Block

Block Diagram

Wiring Diagrams

RS485

RS422

RS232 (terminal block)

RS232 (DB9)

Note

Jumpers are available for scenarios where non-criss-crossing DB9 cables are being used. See RS232 DB9 Jumper Pairs for more information on how to use Serial Tap Pro’s DB9 jumper pairs.

Warning

A common misuse is attempting to connect RS485 devices equipped with DB9 connectors directly into Serial Tap Pro’s DB9 ports. Serial Tap Pro’s DB9 connectors are not designed to interface directly with RS485 devices. Doing so can result in improper operation or even damage to the equipment. Instead, use appropriate breakout cables or adapters that match the pinout and electrical characteristics required for safe and effective monitoring.

UART (TTL) 5V

UART (TTL) 3V3

UART (TTL) VEXT

Note

When using VEXT, voltage is determined by the power source connected to the VEXT pinout.

Injection Jumpers

Serial Tap Pro allows injection of data directly into serial lines. However, in order for you to be able to inject via the Serial Tap Pro plugin, as demonstrated here, you will first need to put the relevant jumper for the serial line you wish to inject into to an ON position. By default, all jumpers are OFF.

The tap features 8 injection jumpers, 1 for each serial line. Each injection jumper has a red jumper cap. To enable injection for that line, orient the cap so that it sits on both pins (ON). For example, if you wanted to inject into the tap’s D1 line, you would set the D1 jumper (J11) to the ON position.

Injection Jumpers

Jumper	Interface	Injection Line
J2	RS232	DTR
J3	RS232	RTS
J4	RS232	TX
J5	TTL	DTR
J6	TTL	RTS
J7	TTL	TX
J11	RS485	D1
J12	RS485	D2

Warning

Due to potential collision, when only sniffing, please ensure injection jumpers are set to OFF.

Warning

When injecting to RS232, please ensure that jumper pairs are not set to “LOOPBACK”.

Note

When using RS485/RS422 injection with the injection jumper OFF, IO Ninja will still log outbound packets as if they were transmitted. However, in this mode, the data is not actually sent on the physical bus. This differs from RS232 and TTL interfaces, where injection is gated by jumper state and transmission is inhibited when the jumper is OFF.

This behavior is by design and reflects a fundamental characteristic of RS485 buses: they are half-duplex by nature. Unlike RS232 or TTL, RS485 does not allow simultaneous transmission and reception on the same pair of lines. Consequently, the Serial Tap Pro cannot verify whether a packet was physically transmitted when the injection jumper is OFF. For consistency and clarity, IO Ninja always logs attempted transmissions on RS485 interfaces, regardless of jumper configuration. This is not a bug or limitation, rather, it is an inherent aspect of how RS485 injection is implemented in hardware.

RS232 DB9 Jumper Pairs

Serial Tap Pro has an additional useful feature allowing you to swap and loopback the signals in TX/RX, RTS/CTS, and DTR/DSR signal pairs. To achieve this, two jumpers are provided for each of the three pairs. There are three standard jumper configurations:

• NORMAL — In this position, the lines are arranged in such a way that wedging the Tap between the serial devices does not change anything. Meaning, TX on one end goes to RX on another end, and vice versa. This mode will work for most scenarios.

• SWAP — This swaps signals in a pair. Meaning, TX goes to TX, and RX goes to RX. Sometimes DB9 cables don’t do criss-crossing, so criss-crossing can be achieved this way instead.

• LOOPBACK — Both serial devices “receive back” their own signals. Meaning, the TX line on each side “comes back” through the RX line.

The following diagram illustrates the jumper arrangements. The diagram shows the jumpers for the TX and RX signal pair. RTS/CTS and DTR/DSR jumpers work in the same way.

Warning

When injecting to RS232, please ensure that jumper pairs are not set to “LOOPBACK”.

RS485 Data Direction Detection

Serial Tap Pro features RS485 data direction detection, enabling you to precisely identify which device on a RS485 bus is transmitting at any given moment. In typical half-duplex RS485 configurations, all nodes share a single differential pair, which makes determining the origin of a message difficult. Serial Tap Pro addresses this by inserting itself in-line between two physical points on the RS485 bus. It connects to the differential pairs D1+/D1− and D2+/D2−. Acting as a transparent man-in-the-middle, its FPGA core actively forwards data between these two bus segments. This approach ensures that for every byte received, the FPGA knows whether it came from the D1 or D2 side, allowing it to infer the sender’s direction without relying on protocol decoding or timing heuristics. Thanks to this method, RS485 data direction detection works at the physical layer, independent of the protocol being used in the session. An example is shown below:

Using Serial Tap Pro

Basic Setup

1. Ensure your Serial Tap Pro is connected to your serial device and your computer.

Note

Please see the Wiring Diagrams section for guidance on connecting your tap.

2. In IO Ninja, click the “New Session” dropdown and select a new “Serial Tap Pro” session.

3. If not selected automatically, select your Serial Tap Pro from the “Tap:” dropdown.

Note

If you can’t see your tap, press the “Refresh” button.

4. Adjust settings as needed via the “Settings” button (see “Settings” section below for details).

Note

Before capturing, you should select the proper baud rate (and other serial parameters). If you need to set a non-standard baud rate, you can type it in directly to the “Baud rate” input field.

5. Start capturing by clicking the “Capture” button located to the right of the “Tap:” dropdown.

Note

If you encounter permission denied errors on Linux, please see this knowledge base article.

6. Monitor traffic in the “Serial Tap Pro” tab.

7. If you wish, add a layer such as Modbus Analyzer for easier analysis.

Flipping Line Directions

When tapping into bi-directional serial lines, it is not always obvious which direction the data is flowing, e.g., which side is transmitting (TX) and which is receiving (RX). Depending on how your tap wires are physically connected, the traffic may appear reversed in the log view. This can make it difficult to interpret which endpoint initiated a message and which replied. To address this, the Serial Tap Pro plugin includes a “Flip line directions” checkbox in the “Serial Tap Pro log” section of the “Control” pane. When this option is enabled, the plugin inverts the logical direction of the lines. What was previously displayed as TX will now appear as RX, and vice versa. The same flipping applies to control lines like DTR/DSR and RTS/CTS.

Note

Enabling the “Flip line directions” setting only affects the view of data inside IO Ninja, nothing on the Serial Tap Pro itself, or its redirect lines are physically changed.

Separating Bytes

Serial Tap Pro captures microsecond-precision hardware timestamps for each byte, but to actually see these individual time stamps inside IO Ninja, you must enable “Separate bytes” via “Settings”, or through checking “Separate bytes” in the “Serial Tap Pro log” section of the “Control” pane.

Injecting Packets

1. Ensure the jumper for the serial interface/line you are using, e.g. D1 or D2 is ON.

2. Ensure “Serial Tap Pro injection” in the “Control” pane is enabled.

3. In the “Serial Tap Pro injection” section, you are able to select the “Mode” and the line you wish to inject to for RS485/RS422, and given the option to select from DTR or RTS for RS232/TTL.

Note

In RS485/RS422 mode, Serial Tap Pro colors data from D1 blue and from D2 green. Since injected data shares the same line as captured data, it would normally appear in the same color, making it hard to distinguish. To fix this, the “Mode” dropdown in the Injection Panel controls how the FPGA emits notification codes for injected bytes, affecting their color in the log.

• Half-duplex and Half-duplex D1↔D2

  • In both modes, the FPGA inverts the notification codes for injected bytes — injected data on D1 appears green, and on D2, blue. This helps separate captured vs. injected traffic. The difference between these modes is that “Half-duplex D1↔D2” mode is used for direction detection via forwarding, where the FPGA actively relays data between D1 and D2 bus segments to infer message direction at the physical layer.

• Full duplex

  • In this mode, the FPGA does not invert notification codes, so everything captured on D1 is colored blue, and everything that is captured on D2 is colored green.

Summary

Mode	Line	Captured Byte Color	Injected Byte Color
Half-duplex	D1	Blue	Green
	D2	Green	Blue
Half-duplex D1 ↔ D2	D1	Blue	Green
	D2	Green	Blue
Full-duplex	D1	Blue	Blue
	D2	Green	Green

4. Using the “Transmit” pane, send serial packets just like you would with any serial terminal.

Displaying Parity Bit (9-bit)

Serial Tap Pro supports 9-bit UART communication. The Serial Tap Pro plugin indicates the 9th parity bit using a red overline above the parity bit, making it easy to distinguish at a glance. Traditionally, the parity bit was primarily used for detecting transmission errors. However, in modern applications, especially in 9-bit mode, this extra bit is often repurposed to differentiate between address and data bytes. This 9th bit functionality is useful in multidrop or multipoint serial networks, where a single master communicates with multiple slave devices on the same bus.

1. In the “Serial settings” section of the “Control” pane, select a parity from the “Parity” dropdown.

2. In the “Serial Tap Pro Log” section of the “Control” pane, enable “Parity bit (9-bit).”

3. Check the log to see the parity bit overlined in red.

Settings

Setting	Description	Default
Device	The Serial Tap Pro that should be used.
Baud rate	The serial baud rate.	38400 bps
Data bits	Serial data bit count (word size). See available options.	8 bits
Parity	When enabled, the Serial Tap Pro plugin indicates the 9th parity bit using a red overline above the parity bit, making it easy to distinguish at a glance. See available options.	None
Stop bits	Serial stop bit count. See available options.	1 bit
Read parallelism (Windows-only)	Maximum number of read requests to issue in parallel. Having more than one pending read at a time helps with increasing read throughput when incoming data arrives in rapid streams (after filling one user buffer, the kernel can immediately switch to the next one without any waiting). Increasing this number beyond 4 usually won’t yield any extra performance gains.	4
RX buffer size (B)	The full size of the incoming data (RX) buffer. Affects read throughput.	16KB
TX buffer size (B)	The full size of the outbound data (TX) buffer. Affects write throughput.	1024KB
RX buffer full notifications	Toggle warnings in log about the incoming data (RX) buffer getting full.	False
Flip line directions	Flip the view of bi-directional lines (TX/RX, DTR/DSR, RTS/CTS).	False
Separate bytes	Show each captured byte on a separate line to inspect individual byte timestamps.	False
Parity bit (9-bit)	Mark bytes that have a parity (9-bit) set.	False
Serial setting changes	Toggle notifications about serial setting (baud rate, data size, parity, stop bits, flow control) changes in the log.	True
Serial line changes	Show/hide serial control line changes (TX/RX, DTR/DSR, RTS/CTS).	True
Serial line errors	Toggle warning about serial line errors (PARITY, FRAMING and BREAK) in the log.	True

Data Bit Options

Option
5 bits
6 bits
7 bits
8 bits

Parity Options

Option	Description
None	No parity bit is used
Odd	Odd parity (parity bit is set when the number of logical ones in the UART frame is odd).
Even	Even parity (parity bit is set when the number of logical ones in the UART frame is even).
Mark	Parity bit is present and always set.
Space	Parity bit is present and always clear.
Ignore	Parity bit is enabled, but IO Ninja will not perform any kind of error checking based on parity.

Stop Bit Options

Option
1 bit
1.5 bits
2 bits

Specifications [1] [2]

General Specifications

Parameter	Specification
Interfaces	USB, RS232, RS485/RS422, TTL
Data Storage	Only volatile memory [3]
Terminal Block Recommended Wire Gauge	26AWG to 20AWG
Hardware Timestamping Precision	1us
System Tick (FPGA)	~20ns
Isolation [4]	Power supply and galvanic data isolation upto 2.5kV
ESD Compliance	8kV
Storage Temperature	-40°C to +85°C
Operating Temperature	0°C to +70°C
Operating Humidity (MIL standard)	0% to 90% non-condensing
Mechanical Dimensions	82 x 74 x 30 mm
Weight (with accessories and packaging)	TBD
Product Net Weight	TBD
CE/UKCA/FCC/ISED Compliance	In progress
RoHS	Compliant
Software Support	IO Ninja 5.7.6 and above

USB Interface

Parameter	Specification
USB Class	USB 2.0 device, full-speed
Connector	USB-C
Nominal Average Current Consumption	300mA
Protections	Galvanic isolation, ESD protection
Vendor ID	0x326F
Product ID	0x0005

RS232 Interface

Parameter	Specification
Available Connectors	Terminal block and DB9
Maximum Baud-rate	2.5Mbps
Protections	ESD, isolation from USB interface, noise damping on shield connectors [5]
Injection	Available for TX, RTS and DTR through hardware jumpers J2, J3, and J4

TTL Interface

Parameter	Specification
Available Connectors	Terminal block
Maximum Baud-rate	2.5Mbps
Injection	Available for TX, RTS and DTR through hardware jumpers J5, J6, and J7
TTL Reference Voltage	Internal (3.3V or 5V) or external voltage via VEXT input [6]
Minimum TTL Reference Voltage	1.8V
Maximum TTL Reference Voltage	5V
Protections	ESD, isolation from USB interface, noise damping on shield connectors, overvoltage and surge protection

RS485 Interface

Parameter	Specification
Available Connectors	Terminal block
No. of Channels	2 buses (D1 and D2)
Maximum Baud-rate	2 Mbps
Injection	Available for both D1 and D2 via hardware jumpers J11 and J12.
Protections	ESD, isolation from USB interface, ESD, ±65V fault protection on D1 and D2 interface, Reverse polarity protection

Package Contents

• Serial Tap Pro

• USB-C cable

• Two DB9 gender changers

Footnotes

[1]

All specifications are subject to change without notice and are for reference only. Tibbo assumes no responsibility for any errors in this Manual and does not make any commitment to update the information contained herein.

[2]

Is the data you are looking for missing from the specifications table? Do not just assume that you know the answer — talk to Tibbo! Remember, that the ultimate responsibility for all decisions you make regarding the use and the mode of use of Tibbo products lies with you, our Customer.

[3]

Serial Tap Pro does not contain any non-volatile memory onboard for captured data and no interfaces for connecting to external storage devices such as USB flash drives, memory cards, CD drives, or similar. The USB port on the device serves solely as a communication channel to the host PC running the IO Ninja software. Therefore, as sold, this product does not include any mechanism for storing or retaining customer data, including, but not limited to, the contents of intercepted serial communications. This characteristic makes the device suitable for use in environments with strict data security requirements, such as governmental or sensitive engineering facilities.

[4]

Electrical isolation is between USB and RS232/RS485 and TTL interfaces. Serial interfaces are not isolated from each other and they all share the same ground line as exposed on terminal block and pin #5 of both DB9 connectors.

[5]

The outer shell of DB9 connectors (shield) are connected to each other via PCB and they have surge arrestor (damping) circuitry on them. They are not connected neither to the ground of the USB nor the isolated ground.

[6]

Onboard 3V3 and 5V reference voltages exist and can be set by TTL jumper. If another voltage is needed, it should be supplied via VEXT. There is protection for overvoltage above 5V on the VEXT and TTL signals.