Is RAM always readable

ram

I am currently interfacing with a temperature sensor (MLX90616) which stores data in certain ram addresses which can be accessed.
I am interested in looking at the raw IR data as opposed to the calculated object or ambient temperature. This would involve accessing addresses 0x004 and 0x005 which have not been indicated as readable on the table below from the datasheet.

my question therefore is if RAM always readable? or does it depend on the device.
if so why would a manufacture not indicate that these addresses are readable on the datasheet?

Best Answer

The part you're using has an SMBus interface, so the question is not one of whether RAM is readable, but rather whether or not the device will let you read specific addresses.

The answer is that it's entirely up to the design of the specific device, and no general rule applies here. If the datasheet does not list the address as readable, the device may or may not return it if queried - and if it does, that could change at any time with newer revisions.

Related Solutions

Electronic – 256X8 RAM chip question

256x8 = 256 cells that hold 8 bits each, so the total capacity of that chip is 256 bytes (or 2048 bits). 4096/256=16

Electronic – using ram verilog instantiation

You'll need to use the clock to break up the write and read operations. Here is an example of a test bench that writes data to two addresses then reads them back.

wire [DATA_WIDTH-1:0] data = we ? wdata : {DATA_WIDTH{1'bz}}; // tri-state write output driver
ram i_ram0(clk,we,addr,data);

initial begin
  clk   = 1'b1;
  data1 = 'h0F;
  data2 = 'hF0;
  addr1 = 0;
  addr2 = 2;
  we    = 1'b1;
  addr  = addr1;
  wdata = data1;
  @(posedge clk) #1;
  addr  = addr2;
  wdata = data2;
  @(posedge clk) #1;
  we    = 1'b0;
  addr  = addr1;
  @(posedge clk) #1;
  if(data !== data1) $display("ERROR data:%h != data1:%h @ addr:%h", data,data1,addr);
  addr  = addr2;
  @(posedge clk) #1;
  if(data !== data2) $display("ERROR data:%h != data2:%h @ addr:%h", data,data2,addr);
  @(posedge clk) #1;
  $finish;
end

FLY if data is an inout, then you need a tri-state driver in your ram module:

assign data = we ? {DATA_WIDTH{1'bz}} : rdata; // tri-state read output driver

Full working example here: http://www.edaplayground.com/s/6/221

Best Answer

Related Solutions

Electronic – 256X8 RAM chip question

Electronic – using ram verilog instantiation

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