LCD Keypad and some more Address space

Hi all,

I am trying to do something which I suspect is rather easy, but must be missing something. I have an RCM3700 module and have hooked it up to the standard LCD display used by most of the eval kits. Backlight, 7 LED’s etc etc.

My question is simple. Having done this I notice that the LCD itself uses all 8 data bus lines, and all 5 address bus lines available at the header connector; I want to hook up some logic other than this and get the core module to read data over its 8bit bus, (no problem) using some unused address on the address bus. Using 5 bits of address bus I only have 32 bytes of addressable space!

Does the LCD panel / keypad use all the 5 bits of address for control?

Are there any spare addresses in these lines left over?

Just for clarity, and stating the obvious no doubt, the connections to the LCD display / keypad are:-

PA0…PA7 (The AUX IO data bus)
PB2…PB5 and PB7 ( The AUX Address bus lines )

I am looking for an address on the PB? lines that is not used so I could enable some data on the bus without effecting the LCD panel.

I hope that question is clear, if not feel free to come back to me


Hi Dave,

As it happens you can use the 5 or as many address lines as you want, up to the maximum, which for the RCM3000 is 8 address lines, some 256 bytes of address space per block. The clever part is the CHIP SELECT that is generated from PORT E. Check the documentation on these pins as this is how you select each 256 byte block.

Hope this makes sense to you?