Printing device

1. A printing device, comprising:

a function adding unit arranged to be detachable,

a display unit for displaying error information of the printing device,

a non-volatile memory for storing device information when said attached function adding unit is selected;

a detection unit for detecting whether the function adding unit is attached when said printing device is turned on, and

a control unit electrically connected to the display unit and the detection unit for requesting the display unit to display the error information when the function adding unit is not attached and said device information is stored in said non-volatile memory.

2. A printing device according to claim 1 , wherein said function adding unit includes a memory unit for storing device information.

3. A printing device according to claim 2 , further comprising a judging unit for judging whether identification information of said printing device to which the memory unit is to be attached stored in the memory unit matches to identification information of the printing device after the detection unit detects that the memory unit is attached.

4. A printing device according to claim 3 , wherein said identification information is a specific number assigned to the printing device.

5. A printing device according to claim 3 , wherein said identification information is a specific number assigned to the memory unit.

6. A printing device according to claim 1 , wherein said function adding unit includes an option functional unit for adding a function to the printing device.

7. A printing device according to claim 1 , wherein said detection unit detects whether the function adding unit is attached when there is information indicating that the function adding unit is attached.

8. A printing device according to claim 1 , wherein said device control unit does not start printing when the device control unit requests the display unit to display the error information.

9. A printing device according to claim 1 , wherein said device information is charging information.

10. A printing device according to claim 1 , wherein said device information is consumption information of a supply.

11. A printing device according to claim 10 , wherein said supply is a developing material.

12. A printing device according to claim 10 , wherein said supply is a developing unit.

13. A printing device comprising:

a function adding unit arranged to be detachable and including a memory unit for storing device information,

a display unit for displaying error information of the printing device,

a detection unit for detecting whether the function adding unit is attached, and

a control unit electrically connected to the display unit and the detection unit for requesting the display unit to display the error information when the function adding unit is not attached, wherein said detection unit detects whether the function adding unit is attached when there is information indicating that a mode is set for storing the device information.

14. A printing device according to claim 13 , wherein said mode is set through a command from an upper device.

15. A printing device according to claim 13 , wherein said mode is set through an operation unit.