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Two-Wire Interface#

Two-Wire Interfaceカメラ機能を使用すると、2線式インターフェース（TWI）バスを介して、カメラと1つまたは複数の外部デバイスの間でデータを転送できます。

例えば、カメラを使用して、TWI対応レンズのフォーカスを制御できます。

機能を使用する#

仕組み#

TWIバスは2線式バスで、1本のシリアルデータライン（SDA）と1本のシリアルクロックライン（SCL）で構成されています。これらは双方向ラインです。

カメラ（マスター）と外部デバイス（スレーブ）は、データラインとクロックラインの両方に接続されています。データは、データラインを介してカメラにより送信、または要求、取得されます。クロックラインはクロック信号の送信に使用され、カメラによって制御されます。

Two-Wire Interface図

上記のTWIインターフェースを使用するには、カメラのGenICamパラメーターがスレーブデバイスの仕様に準拠している必要があります。

適切な通信プロトコルの実装に役立つカメラパラメーターを以下に示します。

TWI通信の設定#

カメラと外部デバイスの間のTWI通信を設定するには、次の手順を実行します。

  1. Set the BslTwiBitrate parameter to the bit rate you want to use for TWI, e.g., 50 kbps.
  2. カメラの入出力信号を設定します。
    1. Set the LineSelector parameter to the I/O line that should write and read serial data, e.g., Line2. The line must be configured as an input-output line.
    2. Set the BslLineConnection parameter to TwiSda.
    3. Set the LineSelector parameter to the I/O line that should be used for sending clock signals, e.g., Line3. The line must be configured as an input-output line.
    4. Set the BslLineConnection parameter to TwiScl.

データの書き込みと読み取り#

TWI通信を設定した後は、外部デバイスへのデータの書き込みと読み取りが可能です。

パラメーターの書き込みと読み取り#

次のパラメーターが、データの書き込みと読み取りの両方に関係します。

  • BslTwiTransferBuffer: The transfer buffer holds the data to be written, and also contains the data that has been read. It can hold up to 16 bytes.
  • BslTwiTransferLength: Indicates the number of bytes that should be transmitted from or to the transfer buffer. When writing, the transfer length specifies the number of bytes the camera should transmit per transaction. When reading, it specifies the number of bytes the camera has received during the last transaction. The maximum value is 16.
  • BslTwiTargetAddress: Indicates the 7-bit target address of the external slave device.

次のパラメーターがデータの書き込みに関係します。

  • BslTwiWrite: Execute this command to write the number of bytes specified by the transfer length from the transfer buffer to the target address of the slave device.

次のパラメーターがデータの読み取りに関係します。

  • BslTwiRead: Execute this command to read or retrieve the data from the target address of the slave device. The number of bytes read is specified by the transfer length.

転送ステータス#

The transfer status indicates the current status of the data transmission. When the transmission has been completed successfully, the transfer status indicates Success. To retrieve the current transfer status, update the transfer status by executing the BslTwiUpdateTransferStatus command and then get the value of BslTwiTransferStatus.

If the value of BslTwiTransferStatus is Pending, you repeatedly have to update and read the transfer status until the transfer status indicates Success. New data can only be written or read if the transfer status indicates Success.

転送ステータスには、次の値があります。

  • Success: The latest data transmission was successful.
  • Pending: A data transmission is pending.
  • NAKAddress: The camera didn't receive an acknowledge bit that confirms the target address after the latest write or read command. In this case, data transmission failed.
  • NAKData: The camera didn't receive an acknowledge bit for successful data transmission after the latest write command. In this case, data transmission failed.

I/Oラインを低くする#

Some TWI slave devices require pulling the I/O lines low before starting operation. If you need to pull an I/O line low, set the BslTwiPullSdaLow parameter or the BslTwiPullSclLow parameter or both to true. While one of them is true, data transmission is disabled.

サンプルコード#

// Configure TWI communication
// Set the bit rate to 50 kbps
camera.BslTwiBitrate.SetValue(BslTwiBitrate_Bitrate50kbps);
// Set line 2 to input-output and use it for TWI SDA
camera.LineSelector.SetValue(LineSelector_Line2);
camera.LineMode.SetValue(LineMode_InOut);
camera.BslLineConnection.SetValue(BslLineConnection_TwiSda);
// Set line 3 to input-output and use it for TWI SCL
camera.LineSelector.SetValue(LineSelector_Line3);
camera.LineMode.SetValue(LineMode_InOut);
camera.BslLineConnection.SetValue(BslLineConnection_TwiScl);
// Now, you must implement a suitable communication protocol.
// Camera parameters that help you implement the protocol are listed
// in the "Writing and Reading and Data" section above.

INodeMap& nodemap = camera.GetNodeMap();
// Configure TWI communication
// Set the bit rate to 50 kbps
CEnumParameter(nodemap, "BslTwiBitrate").SetValue("Bitrate50kbps");
// Set line 2 to input-output and use it for TWI SDA
CEnumParameter(nodemap, "LineSelector").SetValue("Line2");
CEnumParameter(nodemap, "LineMode").SetValue("InOut");
CEnumParameter(nodemap, "BslLineConnection").SetValue("TwiSda");
// Set line 3 to input-output and use it for TWI SCL
CEnumParameter(nodemap, "LineSelector").SetValue("Line3");
CEnumParameter(nodemap, "LineMode").SetValue("InOut");
CEnumParameter(nodemap, "BslLineConnection").SetValue("TwiScl");
// Now, you must implement a suitable communication protocol.
// Camera parameters that help you implement the protocol are listed
// in the "Writing and Reading and Data" section above.

// Configure TWI communication
// Set the bit rate to 50 kbps
camera.Parameters[PLCamera.BslTwiBitrate].SetValue(PLCamera.BslTwiBitrate.Bitrate50kbps);
// Set line 2 to input-output and use it for TWI SDA
camera.Parameters[PLCamera.LineSelector].SetValue(PLCamera.LineSelector.Line2);
camera.Parameters[PLCamera.LineMode].SetValue(PLCamera.LineMode.InOut);
camera.Parameters[PLCamera.BslLineConnection].SetValue(PLCamera.BslLineConnection.TwiSda);
// Set line 3 to input-output and use it for TWI SCL
camera.Parameters[PLCamera.LineSelector].SetValue(PLCamera.LineSelector.Line3);
camera.Parameters[PLCamera.LineMode].SetValue(PLCamera.LineMode.InOut);
camera.Parameters[PLCamera.BslLineConnection].SetValue(PLCamera.BslLineConnection.TwiScl);
// Now, you must implement a suitable communication protocol.
// Camera parameters that help you implement the protocol are listed
// in the "Writing and Reading and Data" section above.

/* Macro to check for errors */
#define CHECK(errc) if (GENAPI_E_OK != errc) printErrorAndExit(errc)
GENAPIC_RESULT errRes = GENAPI_E_OK;  /* Return value of pylon methods */
/* Configure TWI communication */
/* Set the bit rate to 50 kbps */
errRes = PylonDeviceFeatureFromString(hdev, "BslTwiBitrate", "Bitrate50kbps");
CHECK(errRes);
/* Set line 2 to input-output and use it for TWI SDA */
errRes = PylonDeviceFeatureFromString(hdev, "LineSelector", "Line2");
CHECK(errRes);
errRes = PylonDeviceFeatureFromString(hdev, "LineMode", "InOut");
CHECK(errRes);
errRes = PylonDeviceFeatureFromString(hdev, "BslLineConnection", "TwiSda");
CHECK(errRes);
/* Set line 3 to input-output and use it for TWI SCL */
errRes = PylonDeviceFeatureFromString(hdev, "LineSelector", "Line3");
CHECK(errRes);
errRes = PylonDeviceFeatureFromString(hdev, "LineMode", "InOut");
CHECK(errRes);
errRes = PylonDeviceFeatureFromString(hdev, "BslLineConnection", "TwiScl");
CHECK(errRes);
/* Now, you must implement a suitable communication protocol. */
/* Camera parameters that help you implement the protocol are listed */
/* in the "Writing and Reading and Data" section above. */

# Configure TWI communication
# Set the bit rate to 50 kbps
camera.BslTwiBitrate.Value = "Bitrate50kbps"
# Set line 2 to input-output and use it for TWI SDA
camera.LineSelector.Value = "Line2"
camera.LineMode.Value = "InOut"
camera.BslLineConnection.Value = "TwiSda"
# Set line 3 to input-output and use it for TWI SCL
camera.LineSelector.Value = "Line3"
camera.LineMode.Value = "InOut"
camera.BslLineConnection.Value = "TwiScl"
# Now, you must implement a suitable communication protocol.
# Camera parameters that help you implement the protocol are listed
# in the "Writing and Reading and Data" section above.

pylon Viewerを使用して、パラメーターを簡単に設定することもできます。