BeasTTY

A VT52 emulator in the browser, for use with the Feersum Technology MicroBeast z80 retrocomputer.

How do I use it?

Plug in your retrocomputer then visit https://blowback.github.io/beasTTY/ in a Chrome-based browser. Click "Connect" from the menu at the top, select your MicroBeast USB port, and off you go.

I don't like chrome, can I use $BROWSER?

You may not. Only Chrome supports WebSerial, upon which this TTY is based.

Display styles

Render a crisp modern display with "Clean" or go for a more vintage CRT look with "Green", "Amber", "White", "Blue" or "Red".

The special "Graphics Mode" characters are not available in "Clean" mode, which uses Jetbrains Mono Regular or falls back to whatever monospaced font is locally available.

CRT Fonts

As well as it's own builtin 16x8 font, the TTY includes a version of the original VT52 font, including the special "Graphics mode" characters accessible by ESC F. This font comes from the fritzm/vt52 github repo.

The fonts Cushion, Insigbyte, You Squared, Chit, Orbiter, Patrol, Striker and ZX Palm all come from the excellent ZX Origins where there are many many more examples of DamienG's meticulous work.

Keyboard shortcuts

All shortcuts are intercepted only when the terminal area has focus. Bare keys (no modifier listed) encode normally to the host as VT52 bytes — the table only lists chords and special keys with UI-side meaning.

UI / clipboard

Shortcut	Action
Ctrl+Alt+T	Toggle theme (CRT ↔ Clean)
Ctrl+= / Ctrl++	Zoom in (1× → 4×)
Ctrl+-	Zoom out
Ctrl+0	Reset zoom to 1×
Ctrl+Shift+C	Copy current selection to clipboard
Ctrl+Shift+V	Paste from clipboard (subject to rate limit)
Ctrl+Shift+Esc	Clear an established selection
Drag files onto canvas	Open SLIDE send modal for the dropped files
Click ↑ Send file (top bar)	Open file picker for SLIDE send
Esc (during SLIDE transfer)	Cancel the in-flight SLIDE send or receive

Scrollback navigation

Shortcut	Action
Shift+PageUp	Scroll back one page
Shift+PageDown	Scroll forward one page
Shift+Home	Jump to oldest scrollback line
Shift+End	Snap to live tail (cancel scroll-back)

Any keypress that produces an outbound byte while scrolled-back also snaps the viewport to the live tail before the byte is sent.

Command line history

Shortcut	Action
Up / Down	Activate command line history
Enter	Send the selected command immediately
TAB	Edit the selected command before sending
Esc	Dismiss the command line history popup

Esc key behaviour

Esc is context-sensitive. The first matching rule wins:

Context	Effect of Esc
Ctrl+Shift+Esc (any time)	Clear established selection
Mid-drag (mouse button still down)	Cancel the in-flight selection
Paste pump still running	Cancel paste
Otherwise	Encode 0x1B to host

Browser-reserved chords (cannot be intercepted)

Chromium claims Ctrl+W (close tab), Ctrl+N (new window), Ctrl+T (new tab) and Ctrl+Shift+T (reopen closed tab) at the OS layer. Map those control codes to a different chord on the MicroBeast side if you need them.

File transfer (SLIDE)

BeasTTY supports the SLIDE protocol for sending and receiving files between your computer and the MicroBeast.

Sending files (PC → Z80)

Drag files onto the terminal area, or click the ↑ Send file button in the top menu. The send modal previews each filename rewritten to CP/M 8.3 form, and lets you confirm or cancel the batch before the transfer starts.

If two or more files would collide on the Z80 side after 8.3 truncation (case-insensitive), the modal shows a per-collision-group preview of the auto-rename scheme (REPORT.TXT, REPORT~1.TXT, REPORT~2.TXT, …) and offers three resolutions: Send N renamed, Send only first, or Refuse batch.

By default BeasTTY auto-types A:SLIDE.COM R\r at the Z80 prompt before the transfer to put the Z80 into receive mode. Tell BeasTTY where SLIDE.COM lives in Settings → SLIDE file transfer and it appends the direction letter itself — R here, S when the pull pane asks for files — so one setting serves both directions.

Receiving files (Z80 → PC)

When the Z80 sends a file via A:SLIDE.COM S FILE.TXT, BeasTTY auto-detects the SLIDE wakeup signature (ESC ^ S L I D E) and downloads each file via your browser's Downloads tray. Settings → SLIDE file transfer lets you optionally save received files to a chosen folder instead.

You can also drag filenames from the terminal pane into the filer pane to automatically transfer files from the MicroBeast to your local PC.

NB you can't drag directly to a filer window, you'll just get a new file with all the selected filenames in it!

Beast to beast (two MicroBeasts, two tabs)

If you run two MicroBeasts, open a BeasTTY tab for each and you can copy a file straight from one to the other: select a filename in one beast's terminal and drop it on the other beast's terminal. The source beast pulls the file into its own pull folder, hands the bytes to the other tab, and the destination beast receives them — one gesture instead of a pull, a folder and a send. Nothing leaves your browser; the two tabs talk to each other directly.

Beast-to-beast drag needs both BeasTTY tabs visible at once — use Chrome's Split View to put them side by side.

Both tabs need their own serial port, and the source tab needs a pull folder chosen in its filer pane. If anything is missing you get a plain sentence saying which one thing to fix, not a silent failure.

Cancelling

Press Esc, or click [Cancel] on the floating SLIDE chip, to abort an in-flight send or receive. The wire returns to a clean CP/M prompt.

Checksums

You can generate checksums on the MicroBeast side using my CSUM utility, and compare them with the automatically generated equivalents in BeasTTY'starts filer pane:

Hover over the checksum until the disclosure icon appears:

Click on the disclosure icon to get the multi-block checksum for the file, equivalent to typing csum -v ... on the MicroBeast:

Drag a csum -v ... output from the MicroBeast onto that window to compare it with the local file, block by block:

Working with legacy slide.com (no wakeup)

Detection of inbound transfers and the auto-typed-command handshake both rely on a small patch to the Z80-side slide.asm that emits the 7-byte ESC ^ S L I D E wakeup signature when SLIDE starts up. slide.com versions 0.5.0 and upwards have this support built in.

To use BeasTTY with an unpatched slide.com:

• Sending (PC → Z80): after BeasTTY auto-types the start command (A:SLIDE.COM R\r by default), it waits ~3 s for the wakeup. If nothing arrives, the SLIDE chip switches to Z80 didn't respond. [Retry] [Cancel] [Force start]. Click [Force start] to skip the wakeup wait and begin the transfer anyway — slide.com's receive handshake still works without the signature, you just lose the auto-detection safety net.
• Receiving (Z80 → PC): without the wakeup, BeasTTY can't tell that a SLIDE session is starting, so the inbound bytes hit the terminal parser as garbled output. There is no in-app workaround — you need the patched slide.asm for inbound transfers to work.

If you'd rather make the chip's behaviour explicit (instead of falling into the 3 s timeout each time), set Compatibility mode in Settings → SLIDE file transfer:

• Auto (default) — wait 3 s for the wakeup, then prompt with [Retry] [Cancel] [Force start]. Best when you sometimes use a patched Z80 and sometimes don't.
• Wakeup-required — wait indefinitely for the wakeup signature; never time out. Best when you've patched slide.com and want to be told loudly if the patch isn't loaded.
• Force-start (legacy slide.com) — skip the wakeup wait entirely; jump straight into the transfer the moment auto-type finishes. Best when you're knowingly running stock upstream slide.com.

Settings → SLIDE file transfer

The SLIDE sub-block in the Settings pane covers four prefs. All persist in localStorage.

• Save received files to a chosen folder (off by default) — when on, BeasTTY asks once for a target directory via the File System Access API and writes each subsequent received file there silently, instead of pushing one download per file through the browser's Downloads tray. Off, you get an anchor-click download per file (with a small inter-file gap so Chrome's multi-download throttle doesn't fire).
• SLIDE.COM location (default A: + SLIDE.COM) — a drive dropdown and the program name, saying where SLIDE lives on the device. BeasTTY appends the direction letter and the Enter itself: R to put the Z80 into receive mode before a host-initiated send, S when the pull pane asks the Z80 for files. Stating it once is what keeps the two directions consistent — before this, pulls used a bare SLIDE S and CP/M answered SLIDE? from any drive that wasn't the one holding SLIDE.COM. The .COM is optional (SLIDE works too), and the name need not be SLIDE at all: BeasTTY transfers files with SLIDE specifically, so this names that binary — rename it to BANANA.COM and put that here, and it still speaks the protocol and still takes R/S. (For any other transfer program — XMODEM, YMODEM, KERMIT — you drive the MicroBeast by hand.) The name is validated as a CP/M 8.3 filename; anything else is rejected at use time with a Not a CP/M 8.3 program name — SLIDE won't start. hint, and nothing is typed at the prompt.
• Auto-start SLIDE on the device (default on) — when off, BeasTTY types nothing before a send and you start slide.com on the MicroBeast yourself. The location above still composes the pull command, so dragging files out of the pull pane keeps working either way.
• Show transfer summary chip (default on) — when on, a small chip appears for ~5 s after a successful send or receive completes, reporting the file count, total bytes, and direction (Sent 3 files — 12.4 KB → MicroBeast for sends, Received 2 files — 8.7 KB for receives). Turn it off if you find the post-transfer chip distracting; the chip for cancelled transfers always shows regardless (Cancelled — N of M files transferred), so you'll never silently lose feedback that a cancel actually took effect.
• Compatibility mode (default Auto) — see "Working with legacy slide.com" above.

Can I run it locally?

Yes, download the repo then build it:

scripts/build.sh

then run it with:

python3 -m http.server -d www 8000