Recent days, I come across a situation: there's a decoder, such as SN74LVC138APWR(3-input, 8-output), which uses cpu address pins(A6, A5, A4) as the input signals and LCD_RD_E(LCD pin) as cs signal. Doesn't have any LCD devices on the board. So the question is how can I obtain one of the eight output of decoder.
My thought is activating the LCD_RD_E pin, then write data to the A6A5A4 address and leave all the other cpu address pins to ZERO. However this address must be overlapped with on-chip ram.
So is it right to have the decoder connected like this or how can I arrange the address?
Thanks in advance!