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i2c_master.vhd
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i2c_master.vhd
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--------------------------------------------------------------------------------
--
-- FileName: i2c_master.vhd
-- Dependencies: none
-- Design Software: Quartus II 64-bit Version 13.1 Build 162 SJ Full Version
--
-- HDL CODE IS PROVIDED "AS IS." DIGI-KEY EXPRESSLY DISCLAIMS ANY
-- WARRANTY OF ANY KIND, WHETHER EXPRESS OR IMPLIED, INCLUDING BUT NOT
-- LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A
-- PARTICULAR PURPOSE, OR NON-INFRINGEMENT. IN NO EVENT SHALL DIGI-KEY
-- BE LIABLE FOR ANY INCIDENTAL, SPECIAL, INDIRECT OR CONSEQUENTIAL
-- DAMAGES, LOST PROFITS OR LOST DATA, HARM TO YOUR EQUIPMENT, COST OF
-- PROCUREMENT OF SUBSTITUTE GOODS, TECHNOLOGY OR SERVICES, ANY CLAIMS
-- BY THIRD PARTIES (INCLUDING BUT NOT LIMITED TO ANY DEFENSE THEREOF),
-- ANY CLAIMS FOR INDEMNITY OR CONTRIBUTION, OR OTHER SIMILAR COSTS.
--
-- Version History
-- Version 1.0 11/01/2012 Scott Larson
-- Initial Public Release
-- Version 2.0 06/20/2014 Scott Larson
-- Added ability to interface with different slaves in the same transaction
-- Corrected ack_error bug where ack_error went 'Z' instead of '1' on error
-- Corrected timing of when ack_error signal clears
-- Version 2.1 10/21/2014 Scott Larson
-- Replaced gated clock with clock enable
-- Adjusted timing of SCL during start and stop conditions
-- Version 2.2 02/05/2015 Scott Larson
-- Corrected small SDA glitch introduced in version 2.1
--
--------------------------------------------------------------------------------
LIBRARY ieee;
USE ieee.std_logic_1164.all;
USE ieee.std_logic_unsigned.all;
ENTITY i2c_master IS
GENERIC(
input_clk : INTEGER := 50_000_000; --input clock speed from user logic in Hz
bus_clk : INTEGER := 400_000); --speed the i2c bus (scl) will run at in Hz
PORT(
clk : IN STD_LOGIC; --system clock
reset_n : IN STD_LOGIC; --active low reset
ena : IN STD_LOGIC; --latch in command
addr : IN STD_LOGIC_VECTOR(6 DOWNTO 0); --address of target slave
rw : IN STD_LOGIC; --'0' is write, '1' is read
data_wr : IN STD_LOGIC_VECTOR(7 DOWNTO 0); --data to write to slave
busy : OUT STD_LOGIC; --indicates transaction in progress
data_rd : OUT STD_LOGIC_VECTOR(7 DOWNTO 0); --data read from slave
ack_error : BUFFER STD_LOGIC; --flag if improper acknowledge from slave
sda : INOUT STD_LOGIC; --serial data output of i2c bus
scl : INOUT STD_LOGIC); --serial clock output of i2c bus
END i2c_master;
ARCHITECTURE logic OF i2c_master IS
CONSTANT divider : INTEGER := (input_clk/bus_clk)/4; --number of clocks in 1/4 cycle of scl
TYPE machine IS(ready, start, command, slv_ack1, wr, rd, slv_ack2, mstr_ack, stop); --needed states
SIGNAL state : machine; --state machine
SIGNAL data_clk : STD_LOGIC; --data clock for sda
SIGNAL data_clk_prev : STD_LOGIC; --data clock during previous system clock
SIGNAL scl_clk : STD_LOGIC; --constantly running internal scl
SIGNAL scl_ena : STD_LOGIC := '0'; --enables internal scl to output
SIGNAL sda_int : STD_LOGIC := '1'; --internal sda
SIGNAL sda_ena_n : STD_LOGIC; --enables internal sda to output
SIGNAL addr_rw : STD_LOGIC_VECTOR(7 DOWNTO 0); --latched in address and read/write
SIGNAL data_tx : STD_LOGIC_VECTOR(7 DOWNTO 0); --latched in data to write to slave
SIGNAL data_rx : STD_LOGIC_VECTOR(7 DOWNTO 0); --data received from slave
SIGNAL bit_cnt : INTEGER RANGE 0 TO 7 := 7; --tracks bit number in transaction
SIGNAL stretch : STD_LOGIC := '0'; --identifies if slave is stretching scl
BEGIN
--generate the timing for the bus clock (scl_clk) and the data clock (data_clk)
PROCESS(clk, reset_n)
VARIABLE count : INTEGER RANGE 0 TO divider*4; --timing for clock generation
BEGIN
IF(reset_n = '0') THEN --reset asserted
stretch <= '0';
count := 0;
ELSIF(clk'EVENT AND clk = '1') THEN
data_clk_prev <= data_clk; --store previous value of data clock
IF(count = divider*4-1) THEN --end of timing cycle
count := 0; --reset timer
ELSIF(stretch = '0') THEN --clock stretching from slave not detected
count := count + 1; --continue clock generation timing
END IF;
CASE count IS
WHEN 0 TO divider-1 => --first 1/4 cycle of clocking
scl_clk <= '0';
data_clk <= '0';
WHEN divider TO divider*2-1 => --second 1/4 cycle of clocking
scl_clk <= '0';
data_clk <= '1';
WHEN divider*2 TO divider*3-1 => --third 1/4 cycle of clocking
scl_clk <= '1'; --release scl
IF(scl = '0') THEN --detect if slave is stretching clock
stretch <= '1';
ELSE
stretch <= '0';
END IF;
data_clk <= '1';
WHEN OTHERS => --last 1/4 cycle of clocking
scl_clk <= '1';
data_clk <= '0';
END CASE;
END IF;
END PROCESS;
--state machine and writing to sda during scl low (data_clk rising edge)
PROCESS(clk, reset_n)
BEGIN
IF(reset_n = '0') THEN --reset asserted
state <= ready; --return to initial state
busy <= '1'; --indicate not available
scl_ena <= '0'; --sets scl high impedance
sda_int <= '1'; --sets sda high impedance
ack_error <= '0'; --clear acknowledge error flag
bit_cnt <= 7; --restarts data bit counter
data_rd <= "00000000"; --clear data read port
ELSIF(clk'EVENT AND clk = '1') THEN
IF(data_clk = '1' AND data_clk_prev = '0') THEN --data clock rising edge
CASE state IS
WHEN ready => --idle state
IF(ena = '1') THEN --transaction requested
busy <= '1'; --flag busy
addr_rw <= addr & rw; --collect requested slave address and command
data_tx <= data_wr; --collect requested data to write
state <= start; --go to start bit
ELSE --remain idle
busy <= '0'; --unflag busy
state <= ready; --remain idle
END IF;
WHEN start => --start bit of transaction
busy <= '1'; --resume busy if continuous mode
sda_int <= addr_rw(bit_cnt); --set first address bit to bus
state <= command; --go to command
WHEN command => --address and command byte of transaction
IF(bit_cnt = 0) THEN --command transmit finished
sda_int <= '1'; --release sda for slave acknowledge
bit_cnt <= 7; --reset bit counter for "byte" states
state <= slv_ack1; --go to slave acknowledge (command)
ELSE --next clock cycle of command state
bit_cnt <= bit_cnt - 1; --keep track of transaction bits
sda_int <= addr_rw(bit_cnt-1); --write address/command bit to bus
state <= command; --continue with command
END IF;
WHEN slv_ack1 => --slave acknowledge bit (command)
IF(addr_rw(0) = '0') THEN --write command
sda_int <= data_tx(bit_cnt); --write first bit of data
state <= wr; --go to write byte
ELSE --read command
sda_int <= '1'; --release sda from incoming data
state <= rd; --go to read byte
END IF;
WHEN wr => --write byte of transaction
busy <= '1'; --resume busy if continuous mode
IF(bit_cnt = 0) THEN --write byte transmit finished
sda_int <= '1'; --release sda for slave acknowledge
bit_cnt <= 7; --reset bit counter for "byte" states
state <= slv_ack2; --go to slave acknowledge (write)
ELSE --next clock cycle of write state
bit_cnt <= bit_cnt - 1; --keep track of transaction bits
sda_int <= data_tx(bit_cnt-1); --write next bit to bus
state <= wr; --continue writing
END IF;
WHEN rd => --read byte of transaction
busy <= '1'; --resume busy if continuous mode
IF(bit_cnt = 0) THEN --read byte receive finished
IF(ena = '1' AND addr_rw = addr & rw) THEN --continuing with another read at same address
sda_int <= '0'; --acknowledge the byte has been received
ELSE --stopping or continuing with a write
sda_int <= '1'; --send a no-acknowledge (before stop or repeated start)
END IF;
bit_cnt <= 7; --reset bit counter for "byte" states
data_rd <= data_rx; --output received data
state <= mstr_ack; --go to master acknowledge
ELSE --next clock cycle of read state
bit_cnt <= bit_cnt - 1; --keep track of transaction bits
state <= rd; --continue reading
END IF;
WHEN slv_ack2 => --slave acknowledge bit (write)
IF(ena = '1') THEN --continue transaction
busy <= '0'; --continue is accepted
addr_rw <= addr & rw; --collect requested slave address and command
data_tx <= data_wr; --collect requested data to write
IF(addr_rw = addr & rw) THEN --continue transaction with another write
sda_int <= data_wr(bit_cnt); --write first bit of data
state <= wr; --go to write byte
ELSE --continue transaction with a read or new slave
state <= start; --go to repeated start
END IF;
ELSE --complete transaction
state <= stop; --go to stop bit
END IF;
WHEN mstr_ack => --master acknowledge bit after a read
IF(ena = '1') THEN --continue transaction
busy <= '0'; --continue is accepted and data received is available on bus
addr_rw <= addr & rw; --collect requested slave address and command
data_tx <= data_wr; --collect requested data to write
IF(addr_rw = addr & rw) THEN --continue transaction with another read
sda_int <= '1'; --release sda from incoming data
state <= rd; --go to read byte
ELSE --continue transaction with a write or new slave
state <= start; --repeated start
END IF;
ELSE --complete transaction
state <= stop; --go to stop bit
END IF;
WHEN stop => --stop bit of transaction
busy <= '0'; --unflag busy
state <= ready; --go to idle state
END CASE;
ELSIF(data_clk = '0' AND data_clk_prev = '1') THEN --data clock falling edge
CASE state IS
WHEN start =>
IF(scl_ena = '0') THEN --starting new transaction
scl_ena <= '1'; --enable scl output
ack_error <= '0'; --reset acknowledge error output
END IF;
WHEN slv_ack1 => --receiving slave acknowledge (command)
IF(sda /= '0' OR ack_error = '1') THEN --no-acknowledge or previous no-acknowledge
ack_error <= '1'; --set error output if no-acknowledge
END IF;
WHEN rd => --receiving slave data
data_rx(bit_cnt) <= sda; --receive current slave data bit
WHEN slv_ack2 => --receiving slave acknowledge (write)
IF(sda /= '0' OR ack_error = '1') THEN --no-acknowledge or previous no-acknowledge
ack_error <= '1'; --set error output if no-acknowledge
END IF;
WHEN stop =>
scl_ena <= '0'; --disable scl
WHEN OTHERS =>
NULL;
END CASE;
END IF;
END IF;
END PROCESS;
--set sda output
WITH state SELECT
sda_ena_n <= data_clk_prev WHEN start, --generate start condition
NOT data_clk_prev WHEN stop, --generate stop condition
sda_int WHEN OTHERS; --set to internal sda signal
--set scl and sda outputs
scl <= '0' WHEN (scl_ena = '1' AND scl_clk = '0') ELSE 'Z';
sda <= '0' WHEN sda_ena_n = '0' ELSE 'Z';
END logic;