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POVHDL state machine is not looping
 

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  1. POVHDL state machine is not looping
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    <p>Fellow SO users,</p> <p>I'm programming my ADC (ADC0804 which is mounted on a breadboard connected to a Spartan-3 FPGA board). Now, I'm using this ADC to provide digital output for my humidity sensor. The ADC outputs an 8-bit value which I'm displaying on the LEDs on the FPGA board. </p> <p>Now, I'm writing the state machine in such a way that the ADC would always continue to keep outputting values even when I vary the humidity level. But as for the current implementation I have, eventhough I'm looping back to the first state, I'm not getting a continuous stream of values. I'm only getting one 8-bit value at a time (I.E.; I have to keep pressing the reset button to update the value displayed on the LEDs). The following is my code. </p> <pre><code>FSM_NEXT_STATE_INIT : PROCESS (CLK, RST) BEGIN IF (RST = '1') THEN CURR_STATE &lt;= STARTUP; ELSIF (CLK'EVENT AND CLK = '1') THEN CURR_STATE &lt;= NEXT_STATE; END IF; END PROCESS; START_FSM : PROCESS (CURR_STATE, INTR) BEGIN CASE CURR_STATE IS WHEN STARTUP =&gt; NEXT_STATE &lt;= CONVERT; WR &lt;= '0'; READ_DATA &lt;= '0'; WHEN CONVERT =&gt; IF (INTR = '0') THEN NEXT_STATE &lt;= READ1; ELSE NEXT_STATE &lt;= CONVERT; END IF; WR &lt;= '1'; READ_DATA &lt;= '0'; WHEN READ1 =&gt; NEXT_STATE &lt;= READ2; WR &lt;= '1'; READ_DATA &lt;= '1'; WHEN READ2 =&gt; NEXT_STATE &lt;= STARTUP; WR &lt;= '1'; READ_DATA &lt;= '0'; WHEN OTHERS =&gt; NEXT_STATE &lt;= STARTUP; END CASE; END PROCESS; PROCESS (CLK, RST) BEGIN IF (RST = '1') THEN Y &lt;= (OTHERS =&gt; '0'); ELSIF (CLK'EVENT AND CLK = '1') THEN IF (READ_DATA = '1') THEN Y &lt;= D7&amp;D6&amp;D5&amp;D4&amp;D3&amp;D2&amp;D1&amp;D0; --Concatenate the 8-bit ADC output END IF; END IF; END PROCESS; </code></pre> <p>You'll notice that in state 'READ2', I'm looping back to the beginning (so that I can keep reading values continuously as the states transition) but somehow I don't think this is working. Could anyone please provide some assistance on how to go about solving this?</p>
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    1. USTriple777er
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    1. COQuick rhetorical questions: 1) are you getting stuck in CONVERT because INTR is never asserted? 2) is your FSM going off in the weeds because your reset is not debounced? (you mentioned a reset *button*)
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    2. COHi, INTR is a signal that is asserted by the ADC itself once the conversion is complete. As for the reset button, I'm just using that to manually update the LEDs which output the 8-bit value from the ADC. So, everytime I press the reset button and vary the humidity on the sensor, the value on the LEDs will change.
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      1. USTriple777er
 

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