Release history of Serial Port Utility — new features, UI improvements and fixes.
6.6.1 (2026-08-02)
Features
- Transparent network-to-serial bridge: Link two connections and this machine becomes a serial device server — a program on the network reads and writes the local serial port directly, while both sides of the traffic stay visible on screen. A fast network feeding a slow port is throttled automatically, and whatever still has to be dropped is counted in red until you clear it. Several clients can be handled exclusively, by broadcast, or by taking turns; an address allowlist keeps strangers out, both directions can be recorded into one time-ordered capture file, and a two-minute traffic curve shows how the link is doing
- RFC 2217 and Modbus gateway: Two new protocol modes for the bridge. RFC 2217 lets a remote machine set the baud rate, data format, flow control and control lines as if the port were local; the Modbus gateway converts frames between TCP and RTU, and when several masters share one RS-485 bus it serves them one at a time so every answer goes back to whoever asked
- Selectable wire encodings: Each connection can use its own receive and send encoding (UTF-8, GBK, GB18030, Big5, Shift-JIS, Latin-1, System and more), so a device that speaks GBK no longer arrives as mojibake. Both the settings dialog and the quick-settings panel can change it, and the choice is stored with your settings, the .spu project file and the cloud snapshot; terminal typing and cloud remote send follow the owning connection's encoding too
- Drag the split between connections: The boundary between connections can be dragged, so a busy connection can be given more room; the proportions you drag survive toggling the quick-settings panel
- Custom CRC: The toolbox accepts custom CRC parameters, and the result can be fed straight into the send frame
- Configurable Enter sequence: The bytes sent by Enter in terminal mode are now yours to choose
- Online help center: The Help menu links straight to the online help center
- Restore defaults: Added a guarded workflow for restoring default settings
- Microsoft Store: MSIX packaging is in, so the app can be installed from the Microsoft Store
UI Improvements
- Bridge editor: The six setting groups became three tabs, so the dialog fits a 13" laptop and OK and Cancel are never pushed off screen
- Toolbox: Streamlined the toolbox UI and its window entry
- Quick settings panel: Adding a connection no longer folds the panel away — keeping it open is your call
- Modbus request builder: Removed the empty space at the bottom of the window; it opens at the height the content actually needs
Fixes & Enhancements
- Mac App Store launch crash: The 6.6 build installed from the Mac App Store quit immediately on launch. Fixed, and the release pipeline now has a check that stops the same kind of defect from shipping again
- No way back from TCP/UDP mode: After a connection switched to TCP or UDP, the settings dialog no longer showed the port and mode pickers, leaving no route back to serial mode
- Monospace font on macOS: The default font does not exist on macOS, so it was replaced with a proportional face and the hex and timestamp columns stopped lining up. The font is now picked from what is actually installed
- GB18030 four-byte characters: Fixed the decoding of emoji and similar characters, along with a crash on malformed bytes seen with some Qt builds
- Unencodable characters are no longer swapped silently: A character the current encoding cannot represent is no longer sent as ? — the frame is held back and the status bar names the character
- Smaller install: Dropped an unused database component, cutting roughly 4 MB from the package
6.6.0 (2026-07-19)
Features
- Connection activity lamps: New TX/RX and control-line lamps in the connection group blink as data flows, so you can see at a glance that the link is alive
- Serial control lines: Control lines (DTR/RTS and more) are now supported, with a new Control Lines tab in the settings dialog
- Modbus request builder: A Modbus request builder in the Tools menu — no more hand-crafting frames
- Per-field quick settings: Every group in the quick-settings panel can now be tuned field by field, with the picker moved into the settings dialog
- Append Line Ending and Enter Sends: The send editor can append CR, LF, CRLF or LFCR to each complete message, while terminal typing uses an independent Enter Sends setting; the default remains CR for compatibility
- Restore last connection: The app reopens the connection you were using when you quit, so you can pick up where you left off
- Terminal mode improvements: The terminal shows a caret, and the Tx counter now reports real numbers
UI Improvements
- TCP/UDP mode UI: Polished the TCP/UDP layout and silenced the intrusive server-error popup
- Toolbar: Reworked the log-recording and quick-settings toolbar buttons
- UI alignment & polish: Unified the receive and send rows and aligned the combo boxes
Fixes & Enhancements
- Settings defaults: Fixed missing Log/Display defaults in the settings panel; time formats no longer end up blank
- Session file loading: Fixed some toggle states being lost when loading a .spu session file
- Chinese UI: The data-format options are now labeled Text instead of the misleading "ASCII"
- Log writing: Fixed log writing failing when the log directory did not exist
6.5.6 (2026-07-11)
Features
- Account system: Sign in / sign out from the Account submenu under File, with a "keep me signed in" option; the status bar shows your account state at a glance
- Device binding & account sync: Bind this machine to your account after signing in and keep account data in sync
- Cloud Console: When enabled, a signed-in browser on alithon.com can view this device's ports live; separate "Allow Remote Send" and remote port-control switches govern cloud writes and remote open/close/reconfigure; data uploads only while someone is watching and counts toward the monthly traffic quota
- Auto-reconnect: Automatically tries to reconnect after an unexpected disconnect
- Send-frame checksums: Outgoing frames can carry an automatic checksum, with a quick-settings entry
- Receive find/filter bar: Locate content quickly in large outputs
- Ad-free for licensed users: Status-bar adverts disappear once a licence is activated
UI Improvements
- Toolbar rework: Regrouped by function with connection controls first; toggle buttons now reflect their pressed state; shortcuts completed; the port combo defaults to a real available port; the toolbar is locked in place
- Menu rework: Added a Connection menu, moved Account under File, and consolidated licensing entries; completed Simplified Chinese translations
- Registration dialog: Redesigned the registration/purchase prompt; the defunct Weidian QR code is now a direct purchase link
- Network error dialogs: Friendlier, easier-to-understand error messages
Fixes & Enhancements
- Terminal passthrough: Fixed spaces being sent twice in terminal passthrough mode
- Session file loading: Fixed port selection and console binding being lost when loading a .spu file
- Modification tracking: Fixed the "unsaved changes" flag being wrong after New, and the current file path being overwritten
- Chinese translations: Corrected several translations and disambiguated the "Port" label across contexts
6.5.5 (2026-06-20)
Features
- UDP communication modes: New UDP Server and UDP Client modes with full configuration pages and send/receive support
Fixes & Enhancements
- Received text sanitization: Text receive mode filters out terminal control codes, so garbled symbols no longer pollute the display
- Unified connection settings: Serial, TCP and UDP settings are now managed in one settings panel
- No-port scenario: Fixed the connection mode being misdetected when no serial port is available
- Chinese installer: Fixed the Windows installer build so the setup UI displays Chinese correctly
6.5.4 (2026-06-15)
Fixes & Enhancements
- Adaptive settings panel: Switching to the Log tab now auto-widens a too-narrow window, so settings are no longer clipped
6.5.3 (2026-06-14)
Fixes & Enhancements
- Hardened logging: Fixed a range of logging issues — writing and toggling logs is more reliable
- Status-bar log link: The log path in the status bar is now clickable — it saves and opens the current log file; a placeholder is shown when logging is off, and failures are reported clearly
6.5.2 (2026-06-13)
Fixes & Enhancements
- Major defect sweep: Resolved a batch of defects that affected everyday use
- License activation: Fixed several activation and validation issues, making activation more reliable
- Connection stability: Fixed issues in connection-state detection, the disconnect sequence, and UDP/TCP sending
- Logging: Fixed log toggling and writing when multiple ports are in use
- Checksum calculation: Corrected the CRC-16/USB checksum results
- UI details: Fixed toolbar buttons not showing their selected state; the settings panel now resizes itself when switching tabs
- Transport security: Communication with the server now uses encrypted connections (HTTPS)
6.5.1 (2026-05-27)
Features
- Safer serial text rendering: Non-printable control characters in the receive pane and log output are replaced with placeholders, keeping the UI and logs clean (line breaks, carriage returns and tabs are preserved)
Fixes & Enhancements
- More reliable data saving: Fixed several issues when saving local configuration and license data
- Connection cleanup: Fixed resource release when switching or closing connections, reducing memory growth over long sessions
6.3.1 (2026-03-22)
Features
- AutoFeed improvements: AutoFeed settings are now saved correctly, and the feed interval is configurable
- High-baud-rate support: Unified serial port name display and improved communication at high baud rates
- Adaptive QR codes: QR code images in the license management dialog now scale to fit
Fixes & Enhancements
- Window position memory: Fixed window position and size not being saved and restored correctly
- TCP stability: Fixed occasional TCP connection crashes
- AutoFeed timing: Corrected the AutoFeed time calculation