Gotchas

`connect()` or transport I/O fails

Item	Detail
Symptom	`connect()` fails, a transport call times out, or `TransportError` is returned before a valid SLMP response is parsed.
Root cause	The PLC IP address, port, transport path, or local network route does not match the target.
Fix	Check the PLC endpoint first. The usual SLMP TCP port is `1025`; use UDP only when the PLC is configured for UDP. Increase the timeout only after the endpoint and wiring are known-good.

`BufferTooSmall` is returned

Item	Detail
Symptom	A request fails locally with `BufferTooSmall`.
Root cause	The caller-owned TX/RX buffers are too small for the selected command and point count.
Fix	Increase the TX buffer first for block write, random write, or long password commands. Small direct reads and writes usually fit in `96` bytes; random and block access often need `192..256` bytes.

`ProtocolError` is returned

Item	Detail
Symptom	Bytes are received, but the response is rejected as an invalid SLMP frame.
Root cause	The target endpoint is not speaking the expected SLMP binary frame, or the response length does not match the request.
Fix	Verify the PLC frame setting and inspect `lastRequestFrame()` / `lastResponseFrame()` with `formatHexBytes()`.

GX Simulator 3 uses port 5511 for the default local target

Item	Detail
Symptom	A local GX Works3 simulator connection fails on the hardware default port.
Root cause	GX Simulator 3 uses a simulator port, not the hardware SLMP port. For System `1`, PLC `1`, the port is `5511`.
Fix	Connect to `127.0.0.1:5511` for the default GX Works3 simulator target. GX Simulator 2 uses a proprietary protocol and is not supported by this SLMP library.

LTN/LSTN/LCN/LZ reads return unexpected values

Item	Detail
Symptom	Long timer, long counter, or long index values look truncated or offset.
Root cause	`LTN`, `LSTN`, `LCN`, and `LZ` are 32-bit logical families.
Fix	Read them with `:D` for unsigned 32-bit or `:L` for signed 32-bit.

#include <cstddef>
#include <cstdint>

#include <slmp_high_level.h>
#include <slmp_minimal.h>

class NoopTransport final : public slmp::ITransport {
  public:
    bool connect(const char*, uint16_t) override { return false; }
    void close() override {}
    bool connected() const override { return false; }
    bool writeAll(const uint8_t*, size_t) override { return false; }
    bool readExact(uint8_t*, size_t, uint32_t) override { return false; }
    size_t write(const uint8_t*, size_t) override { return 0U; }
    size_t read(uint8_t*, size_t) override { return 0U; }
    size_t available() override { return 0U; }
};

int main() {
    NoopTransport transport;
    uint8_t tx[128] = {};
    uint8_t rx[128] = {};
    slmp::SlmpClient plc(transport, tx, sizeof(tx), rx, sizeof(rx));
    constexpr auto profile = slmp::highlevel::PlcProfile::IqR;
    slmp::highlevel::configureClientForPlcProfile(plc, profile);

    slmp::highlevel::Value value;
    const slmp::Error err = slmp::highlevel::readTyped(plc, profile, "LTN0:D", value);
    return (err == slmp::Error::Ok || err == slmp::Error::NotConnected) ? 0 : 1;
}

Mixed block write is rejected by the PLC

Item	Detail
Symptom	A block write that mixes word devices and bit devices fails.
Root cause	SLMP command `0x1406` does not accept word and bit blocks in one request on the target PLC path.
Fix	Send word writes and bit writes as separate calls.

#include <cstddef>
#include <cstdint>

#include <slmp_minimal.h>

class NoopTransport final : public slmp::ITransport {
  public:
    bool connect(const char*, uint16_t) override { return false; }
    void close() override {}
    bool connected() const override { return false; }
    bool writeAll(const uint8_t*, size_t) override { return false; }
    bool readExact(uint8_t*, size_t, uint32_t) override { return false; }
    size_t write(const uint8_t*, size_t) override { return 0U; }
    size_t read(uint8_t*, size_t) override { return 0U; }
    size_t available() override { return 0U; }
};

int main() {
    NoopTransport transport;
    uint8_t tx[128] = {};
    uint8_t rx[128] = {};
    slmp::SlmpClient plc(transport, tx, sizeof(tx), rx, sizeof(rx));
    plc.setFrameType(slmp::FrameType::Frame4E);
    plc.setCompatibilityMode(slmp::CompatibilityMode::iQR);

    const slmp::Error wordErr = plc.writeOneWord(slmp::dev::D(slmp::dev::dec(9000)), 1234U);
    const slmp::Error bitErr = plc.writeOneBit(slmp::dev::M(slmp::dev::dec(9000)), true);
    return (wordErr == slmp::Error::NotConnected && bitErr == slmp::Error::NotConnected) ? 0 : 1;
}

G or HG address fails

Item	Detail
Symptom	A normal high-level address such as `G100` or `HG100` does not work as an ordinary device.
Root cause	Module buffer memory is an extended SLMP target, not a normal high-level direct device family.
Fix	Use `slmp::SlmpClient` module-buffer APIs such as `readWordsModuleBuf`.

#include <cstddef>
#include <cstdint>

#include <slmp_minimal.h>

class NoopTransport final : public slmp::ITransport {
  public:
    bool connect(const char*, uint16_t) override { return false; }
    void close() override {}
    bool connected() const override { return false; }
    bool writeAll(const uint8_t*, size_t) override { return false; }
    bool readExact(uint8_t*, size_t, uint32_t) override { return false; }
    size_t write(const uint8_t*, size_t) override { return 0U; }
    size_t read(uint8_t*, size_t) override { return 0U; }
    size_t available() override { return 0U; }
};

int main() {
    NoopTransport transport;
    uint8_t tx[128] = {};
    uint8_t rx[128] = {};
    slmp::SlmpClient plc(transport, tx, sizeof(tx), rx, sizeof(rx));
    plc.setFrameType(slmp::FrameType::Frame4E);
    plc.setCompatibilityMode(slmp::CompatibilityMode::iQR);

    uint16_t words[4] = {};
    const slmp::Error err = plc.readWordsModuleBuf(3, false, 100, 4, words, 4);
    return err == slmp::Error::NotConnected ? 0 : 1;
}

DX or DY fails on iQ-F

Item	Detail
Symptom	`DX` or `DY` is rejected when the selected profile is iQ-F.
Root cause	The iQ-F profile does not support `DX` or `DY` in the high-level parser.
Fix	Use `X` and `Y` with `slmp::highlevel::PlcProfile::IqF`.

#include <cstddef>
#include <cstdint>

#include <slmp_high_level.h>

int main() {
    slmp::highlevel::AddressSpec input{};
    const slmp::Error err = slmp::highlevel::parseAddressSpec(
        "X20",
        slmp::highlevel::PlcProfile::IqF,
        input);
    return err == slmp::Error::Ok ? 0 : 1;
}

Read or write fails because no PLC profile was set

Item	Detail
Symptom	Profile-sensitive addressing, frame type, or compatibility mode does not match your PLC.
Root cause	The helper layer does not probe the PLC and does not infer the profile from model text.
Fix	Choose a concrete `slmp::highlevel::PlcProfile` and call `configureClientForPlcProfile` before communication.

#include <cstddef>
#include <cstdint>

#include <slmp_high_level.h>
#include <slmp_minimal.h>

class NoopTransport final : public slmp::ITransport {
  public:
    bool connect(const char*, uint16_t) override { return false; }
    void close() override {}
    bool connected() const override { return false; }
    bool writeAll(const uint8_t*, size_t) override { return false; }
    bool readExact(uint8_t*, size_t, uint32_t) override { return false; }
    size_t write(const uint8_t*, size_t) override { return 0U; }
    size_t read(uint8_t*, size_t) override { return 0U; }
    size_t available() override { return 0U; }
};

int main() {
    NoopTransport transport;
    uint8_t tx[64] = {};
    uint8_t rx[64] = {};
    slmp::SlmpClient plc(transport, tx, sizeof(tx), rx, sizeof(rx));

    constexpr auto profile = slmp::highlevel::PlcProfile::IqR;
    slmp::highlevel::configureClientForPlcProfile(plc, profile);
    return plc.compatibilityMode() == slmp::CompatibilityMode::iQR ? 0 : 1;
}

High-level helpers are not found by the compiler

Item	Detail
Symptom	Names such as `slmp::highlevel::readTyped` or `slmp::highlevel::Poller` are undefined.
Root cause	`slmp_high_level.h` is optional and is not included by `slmp_minimal.h`.
Fix	Include `slmp_high_level.h` explicitly in any file that uses the high-level facade.

#include <cstddef>
#include <cstdint>

#include <slmp_high_level.h>

int main() {
    slmp::highlevel::AddressSpec spec{};
    const slmp::Error err = slmp::highlevel::parseAddressSpec(
        "D100",
        slmp::highlevel::PlcProfile::IqR,
        spec);
    return err == slmp::Error::Ok ? 0 : 1;
}

Unspecified profile returns an immediate error

Item	Detail
Symptom	Profile-aware helpers return `slmp::Error::InvalidArgument` before any PLC request is sent.
Root cause	`slmp::highlevel::PlcProfile::Unspecified` is not a concrete PLC profile.
Fix	Pass one concrete profile such as `slmp::highlevel::PlcProfile::IqR`.

#include <cstddef>
#include <cstdint>

#include <slmp_high_level.h>

int main() {
    slmp::highlevel::AddressSpec spec{};
    const slmp::Error bad = slmp::highlevel::parseAddressSpec(
        "D100",
        slmp::highlevel::PlcProfile::Unspecified,
        spec);
    const slmp::Error good = slmp::highlevel::parseAddressSpec(
        "D100",
        slmp::highlevel::PlcProfile::IqR,
        spec);
    return (bad == slmp::Error::InvalidArgument && good == slmp::Error::Ok) ? 0 : 1;
}

X or Y string address is rejected

Item	Detail
Symptom	A string address such as `X20` is rejected or maps to the wrong point.
Root cause	`X` and `Y` numbering depends on the PLC profile; iQ-F uses octal, while the other supported profiles use hexadecimal.
Fix	Use the profile-aware overloads of the high-level helpers.

#include <cstddef>
#include <cstdint>

#include <slmp_high_level.h>

int main() {
    slmp::highlevel::AddressSpec spec{};
    const slmp::Error err = slmp::highlevel::parseAddressSpec(
        "X20",
        slmp::highlevel::PlcProfile::IqR,
        spec);
    return err == slmp::Error::Ok ? 0 : 1;
}

D50.D reads bit 13 instead of a 32-bit value

Item	Detail
Symptom	`D50.D` behaves like one bit rather than a double word.
Root cause	Dot notation is bit-in-word access; `D` after the dot is hexadecimal bit index 13.
Fix	Use `D50:D` for unsigned 32-bit data and reserve `D50.D` for bit 13.

#include <cstddef>
#include <cstdint>

#include <slmp_high_level.h>

int main() {
    slmp::highlevel::AddressSpec dword{};
    slmp::highlevel::AddressSpec bit13{};
    const slmp::Error dwordErr = slmp::highlevel::parseAddressSpec(
        "D50:D",
        slmp::highlevel::PlcProfile::IqR,
        dword);
    const slmp::Error bitErr = slmp::highlevel::parseAddressSpec(
        "D50.D",
        slmp::highlevel::PlcProfile::IqR,
        bit13);
    return (dwordErr == slmp::Error::Ok && bitErr == slmp::Error::Ok) ? 0 : 1;
}

Gotchas

connect() or transport I/O fails

BufferTooSmall is returned

ProtocolError is returned

GX Simulator 3 uses port 5511 for the default local target

LTN/LSTN/LCN/LZ reads return unexpected values

Mixed block write is rejected by the PLC

G or HG address fails

DX or DY fails on iQ-F

Read or write fails because no PLC profile was set

High-level helpers are not found by the compiler

Unspecified profile returns an immediate error

X or Y string address is rejected

D50.D reads bit 13 instead of a 32-bit value

`connect()` or transport I/O fails

`BufferTooSmall` is returned

`ProtocolError` is returned