Protocol Driver Limits

Driver limits

Hardcoded in KAREL; working around any of these means editing the source and recompiling.

Limit	Where	Impact
Axis count is a single character	mappdk_cmd.kl, where MOVEJ/MOVEP parse the axis count	Motion commands top out at 9 axes
Server tag is a single character	mappdk_comm.kl, where OPEN_COMM builds the tag string	Only S1 through S9
setsysvar only accepts T/F	SET_SYS_VAR in mappdk_cmd.kl	Numeric system variables need setsysvarnum (extended command)
Response is STRING[254]	mappdk_server.kl, the resp variable declaration	Upper bound on a single response's length
Single connection, synchronous and blocking	mappdk_server.kl, OPEN_COMM/main loop	A server can only serve one client at a time; a motion command blocks until it finishes. The second connection is the logger, see two connections
DIN[] is read-only to user programs	KAREL language level	No way to write/simulate DI from a user KAREL program; ktrans rejects it at compile time regardless of the TP's SIM mode, this path has been abandoned, see below

DIN can't be written or simulated

Tried adding a setdin command that assigns directly to DIN[din_num] on the KAREL side, the same approach as the already working SET_DOUT (mappdk_cmd.kl, which writes DOUT[]), just with DIN being an input array instead. ktrans rejected it outright at compile time:

This system Id is "write protected" from KAREL user programs.  Id: DIN

This isn't "deferred after a risk assessment"; the KAREL language itself simply doesn't allow it: DIN[] is read-only to user programs, entirely independent of whether a point on the TP is set to simulation (SIM) mode (it doesn't even compile, so it never gets that far). DI simulation is only possible through the TP's own operator panel (if the model/version supports it); this package's driver has fully abandoned this path, don't try the same approach again.

RDO out of range aborts the whole server

RDO numbers also used to be read as a single character; numbers 10 and above got truncated to their first digit with no error. This project's driver reads to the end of the string instead; connecting to the upstream driver, the Python side applies the old limit itself.

Accessing an RDO the controller doesn't have aborts the entire MAPPDK_SERVER. The TP shows:

PRIO-002 端口號不正確

Recovering needs RESET and rerunning MAPPDK. KAREL itself can't guard against this: GET_PORT_VAL needs the io_rdo constant, and adding the IOSETUP environment would push past ktrans's limit on the total number of directives plus environments (see extending the driver). So the limit lives in Python instead: protocol.MAX_RDO_NUM defaults to 8, and can be raised by passing max_rdo when constructing FanucRobot. DI and DO carry the same risk.

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Last updated: 2026-08-31