writing instructions to RAM of a microcontroller

[goodpranoy]

hi everyone,

i am presently doing a project "design of a simple functional microcontroller on FPGA".

i have done this with just 2 registers.

to keep the design simple, instead of an I/O port i have designed separate ports for both input and output.

i also used a ROM instead of a RAM.

now i want to convert my ROM into a RAM to which we can write instructions from outside.

how can i do this transition from ROM to RAM?

is the separate input port enough to give both the data and address to the RAM? if so how can i multiplex the signals?

 

[HTA]

one way would be to use the RAM as an instruction storage and load it on power up with the ROM content, which can be altered during operartion or reload also from external.

Enjoy your design work!

 

[rusty81]

Let me understand: have you done a VHDL/Verilog model of a microcontroller over a FPGA, right?

You can make bydirectional ports (like in a real microcontroller) simply declaring a port as "inout" and making a double antiparallel tristate for input/output direction.

A RAM, on a FPGA/CPLD, can be either a real external RAM, or simply an empty array of size equal to ram space that you want.

Cheers