source: firmware/FAD/FACT_FAD_lib/hdl/fad_rs485_definitions.vhd@ 17370

Last change on this file since 17370 was 11755, checked in by neise, 13 years ago
reinit of this svn repos .... it was all too messy deleted the old folders and restarted with FACT_FAD_lib only. (well and the testbenches)
File size: 1.8 KB
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1----------------------------------------------------------------------------------
2-- Company: TU Dortmund, Lehrstuhl fuer experimentelle Physik 5b, Astroteilchenphysik
3-- Engineer: D.Neise
4--
5-- Create Date: April 2011
6-- Design Name:
7-- Module Name: fad_rs485_definitions
8-- Project Name:
9-- Target Devices:
10-- Tool versions:
11-- Description: library file for FAD design
12--
13-- Dependencies:
14--
15-- Revision:
16-- Revision 0.01 - File Created
17--
18-- Additional Comments:
19-- Many thanks to Q. Weitzel
20----------------------------------------------------------------------------------
21
22
23library IEEE;
24use IEEE.STD_LOGIC_1164.all;
25use IEEE.STD_LOGIC_ARITH.ALL;
26-- use IEEE.STD_LOGIC_UNSIGNED.ALL;
27-- use IEEE.NUMERIC_STD.ALL;
28
29package fad_rs485_constants is
30
31 constant FAD_RS485_INPUT_CLK_F : integer := 50000000; -- 50MHz
32 --communication with FTM
33 constant RS485_BAUD_RATE : integer := 250000; -- bits / sec in our case
34 constant RS485_MESSAGE_LEN_BYTES : integer := 7; -- @250kbaud --> 308us in total or (@50Mhz) 15400 clk cycles.
35 -- notes about the timeout:
36 -- the timeout is measured *after* the receiption of the 1st byte ... not after the 1st startbit.
37 -- one byte consists of 1 startbit, 8 databits, 2 stopbit2 --> 11 bits in total.
38 -- in order to have some ~10% contingency, we decided to put 13 bits instead of 11
39 --
40 -- so this timeout evaluates to 18200 clk cycles or 364us *after* the 1st byte was received.
41 -- this means, one message is trunkated only, if it is longer than ~356us in total.
42 -- this might be subject to changes.
43 -- keep in mind that, there is an additional timeout
44 constant RS485_TIMEOUT : integer := (RS485_MESSAGE_LEN_BYTES * 13) * (FAD_RS485_INPUT_CLK_F / RS485_BAUD_RATE);
45
46end fad_rs485_constants;
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