Image forming apparatus having a replacement unit

An image forming apparatus configured to form an image on a sheet, the image forming apparatus comprising:

• a main assembly of the image forming apparatus;
• a replacement unit detachably mounted on the main assembly, the replacement unit includes a sheet detection unit configured to detect passage of a sheet;
• a control unit mounted on the main assembly and configured to control the replacement unit mounted on the main assembly;
• and
• a common signal line connected between the replacement unit mounted on the main assembly and the control unit, the common signal line is a line configured to transmit an identification signal for identifying whether the replacement unit is a first unit or a second unit instead of the first unit and an another signal from the replacement unit to the control unit,
• wherein the control unit switches a control of the replacement unit mounted on the main assembly depending on whether the replacement unit mounted on the main assembly is the first unit or the second unit,
• wherein the control unit is switchable between an identification mode identifies whether the replacement unit mounted on the main assembly is the first unit or the second unit according to the identification signal through the common signal line and a paper detection mode for detecting passage of the sheet according to the another signal output by the sheet detection unit and transmitted through the common signal line,
• wherein the main assembly includes a switch configured to disable detection of a sheet by the sheet detection unit;
• and
• wherein when switching from the paper detection mode to the identification mode, the control unit controls the switch to disable the detection of a sheet by the sheet detection unit.

An image forming apparatus configured to form an image on a sheet, the image forming apparatus comprising:

• a main assembly of the image forming apparatus;
• a replacement unit detachably mounted on the main assembly, the replacement unit includes a sheet detection unit configured to detect passage of a sheet;
• a control unit mounted on the main assembly and configured to control the replacement unit mounted on the main assembly;
• and
• a common signal line connected between the replacement unit mounted on the main assembly and the control unit, the common signal line is a line configured to transmit an identification signal for identifying whether the replacement unit is a first unit or a second unit instead of the first unit and an another signal from the replacement unit to the control unit,
• wherein the control unit switches a control of the replacement unit mounted on the main assembly depending on whether the replacement unit mounted on the main assembly is the first unit or the second unit,
• wherein the control unit is switchable between an identification mode identifies whether the replacement unit mounted on the main assembly is the first unit or the second unit according to the identification signal through the common signal line and a paper detection mode for detecting passage of the sheet according to the another signal output by the sheet detection unit and transmitted through the common signal line,
• wherein in a case where the replacement unit is the first unit, the replacement unit outputs a first signal;
• wherein in a case where the replacement unit is the second unit, the replacement unit outputs a second signal different from the first signal;
• and
• wherein the sheet detection unit outputs the second signal in a case where the sheet detection unit detects a sheet, and outputs the first signal in a case where the sheet detection unit does not detect a sheet.