Fanuc RS-232 settings: parameters, baud rates and alarms
The parameters that decide whether a program transfer works, what the baud-rate codes actually mean, and how to read alarms 085, 086 and 087 — for the person standing at the machine right now.
Before you change anything: write down the current values. Parameter numbering below is the common scheme across the Fanuc 0i, 16i, 18i, 21i and 30i-series families — older 0-M / 0-T controls number things differently, and there are differences between editions. Confirm against the maintenance manual for your exact control, and unlock parameter writing only for as long as you need it.
Step one: which channel is the control using?
Parameter 0020 (I/O CHANNEL)selects the physical port the control reads from and writes to. Every other setting below belongs to a specific channel, so getting this wrong means carefully configuring a port the machine isn't using. If nothing happens at all — no alarm, no data — check this first.
The three settings per channel
Each channel has three parameters: one for the character format, one for the device type, and one for the baud rate.
| Channel | Format (stop bits, code) | Device number | Baud rate code |
|---|---|---|---|
| Channel 1 (JD36A / JD56A) | 0101 | 0102 | 0103 |
| Channel 2 (JD36B / JD36A) | 0111 | 0112 | 0113 |
| Channel 3 | 0121 | 0122 | 0123 |
- Format parameter (0101 / 0111 / 0121): bit flags, of which the stop-bit setting (SB2 — 2 stop bits when set) and the feed/code flags are the ones that matter for a PC connection.
- Device number (0102 / 0112 / 0122): what kind of device is on the other end. Set 0 for a plain RS-232 connection to a PC or a serial device server — the other values are for Fanuc's own cassette adaptors, program file units and tape readers.
- Baud rate code (0103 / 0113 / 0123): a code, not a number. See the table below.
Baud rate codes
This is the table people come looking for, because entering "9600" into the baud rate parameter does not do what it looks like it does.
| Value in the parameter | Actual baud rate |
|---|---|
| 1 | 50 baud |
| 2 | 100 baud |
| 3 | 110 baud |
| 4 | 150 baud |
| 5 | 200 baud |
| 6 | 300 baud |
| 7 | 600 baud |
| 8 | 1200 baud |
| 9 | 2400 baud |
| 10 | 4800 baud |
| 11 | 9600 baud |
| 12 | 19200 baud |
In practice: 10 (4800) and 11 (9600) cover most machines. 12 (19200)is worth trying on a short, clean cable run, but a noisy panel will make it drop characters where 9600 runs all day. Faster is not better if it isn't reliable — for drip-feed, reliability is the whole game.
A working starting point
- Baud rate: 9600 (code 11). Drop to 4800 (code 10) if you see errors.
- Data bits / parity / stop bits: 7 data bits, even parity, 2 stop bits is the classic Fanuc combination; 8/N/1 is also widely used. Match whatever the control is set to rather than imposing a preference.
- Code: ISO, not EIA, unless you have a specific reason.
- Flow control: XON/XOFF (DC1/DC3) enabled on both ends. This is non-negotiable for drip-feed.
- Device number: 0, for a PC or a serial device server.
Whatever you choose, the converter and the PC software must be set identically. The converter buying guide covers which units let you set all of this and which quietly don't.
Transfer alarms and what they mean
These three cover the large majority of failed transfers. On newer controls the same codes appear with an SR prefix — SR0085, SR0086, SR0087 — and mean the same things.
085 — Communication error (overrun / framing / parity)
What it means: Characters arrived faster than the control could take them, or arrived in a shape it didn't expect. Nearly always a settings mismatch rather than a fault.
What to check: Check baud rate, data bits, parity and stop bits match on both ends — control, converter, and PC. Try one step slower on baud; a long cable or a noisy panel can make 19200 unreliable where 9600 is solid.
086 — DR signal off
What it means: The DR (data set ready) line from the I/O device went off, so the control thinks nothing is connected. This is a wiring or power problem, not a data problem.
What to check: Check the cable pinout against the control's manual, that the converter is powered, and that the handshake lines are wired or looped back as the manual requires. A cable that works on one machine can still be wrong for another series.
087 — Buffer overflow / stop bit not detected
What it means: The control asked the sender to stop and it kept sending. Flow control isn't reaching the PC — the classic drip-feed failure, and the one that only shows up on long programs.
What to check: Enable XON/XOFF on the control, the converter and the software. If the converter offers RTS/CTS as well, wire it through. Then re-test with a genuinely long program, not a short one.
A diagnostic order that saves time
- Punch a program out of the machine to the PC first. Receiving proves wiring and settings without risking anything in the control.
- Garbage characters? Baud rate, then parity. Nothing at all, no alarm? Pinout, or the wrong I/O channel.
- Works one direction only? Wiring — a settings mismatch would break both.
- Short files fine, long files fail? Flow control. That's alarm 087 territory, and it's the failure that waits until minute forty of a cut.
- Only change one thing at a time, and write down what you changed. Two simultaneous changes turn a ten-minute fix into an afternoon.
Read next
Drip-feeding programs bigger than control memory, program transfer over Ethernet, or what DNC means if you're new to the term. To test a new link without risking anything in the control, pull a program out of the machine first.
Questions
What are the standard Fanuc RS-232 settings?
The most common working combination for a PC connection is 9600 baud, 7 data bits, even parity, 2 stop bits (7/E/2), ISO code, XON/XOFF flow control — with 4800 baud used on older controls. There is no universal default: what matters is that the control, the converter and the software all agree.
Which parameter sets the baud rate on a Fanuc?
On the 0i / 16i / 18i / 21i / 30i families the baud rate is a code in the third parameter of the I/O channel you're using — 0103 for channel 1, 0113 for channel 2, 0123 for channel 3. The code is not the number: 10 means 4800, 11 means 9600, 12 means 19200.
What is the I/O CHANNEL parameter?
Parameter 0020 selects which physical channel the control uses for input and output. If transfers do nothing at all despite correct settings, this is the first place to look — the settings you carefully changed may belong to a channel the control isn't using.
Why does transfer work in one direction only?
Sending but not receiving (or the reverse) is almost always cable pinout — one of TX/RX is not landing where the control expects it. Settings mismatches usually break both directions, so a one-way link points at wiring.
Should I use ISO or EIA code?
ISO for anything modern. EIA is the older punched-tape character set and is still selectable on old controls; if your output looks like the right program in the wrong alphabet, this is the setting to check.
Do these parameter numbers apply to my machine?
They are the common numbering across the 0i, 16i, 18i, 21i and 30i-series families. Older 0-M and 0-T controls use a different scheme, and there are edition-to-edition differences. Always confirm against the maintenance manual for your exact control before changing a parameter.