Patent ID: 7551166

Claim:
A display device having a light-emitting element and expressing gray scale with a length of lighting time, comprising: a control circuit comprising: first to fourth signals; first and second memories; a reading device; and a writing device, wherein the first signal is a vertical synchronizing signal, wherein the second signal is a horizontal synchronizing signal, wherein the third signal selects roles of the first and the second memories from writing and reading according to timing provided from the first signal and switches the roles of the first and the second memories every start of a writing signal, wherein the fourth signal is determined according to states of the writing signal and the second horizontal synchronizing signal, wherein a state of the fourth signal is changed from a first stand-by state for reading to a readable state when the writing signal is in a writable state and the second horizontal synchronizing signal is inverted, wherein the state of the fourth signal is changed from the readable state to a second stand-by state for reading when the writing signal is in a writable state and the third signal is inverted, and wherein the reading device and the writing device are synchronized in the case where the first memory has a role of reading and the second memory has a role of writing or in the case where the first memory has a role of writing and the second memory has a role of reading.