1/8/ L23 Project Step 9 - Sequential Machine Copyright Joanne DeGroat, ECE, OSU1 Project Step 9 Beyond the ALU and Datapath. Sequential Machine Modeling exercise.

1/8/ L23 Project Step 9 - Sequential Machine Copyright Joanne DeGroat, ECE, OSU2 The sequential machine modeling style  In the lecture on state machine modeling introduces how three processes can be used to model the state machine.  This style is good for documentation, simulation, and synthesis.  And it also maps across multiple HDLs.

1/8/ L23 Project Step 9 - Sequential Machine Copyright Joanne DeGroat, ECE, OSU3 The machine to be modeled  This exercise is to model a Successive Approximation A-to-D converter.  This also introduces the ability of VHDL to model mixed signal systems at a high level of abstraction.

1/8/ L23 Project Step 9 - Sequential Machine Copyright Joanne DeGroat, ECE, OSU4 More on the controller  Modeling to the SAR Controller and SAR Control Register This is the heart of a successive approximation A-to-D unit

1/8/ L23 Project Step 9 - Sequential Machine Copyright Joanne DeGroat, ECE, OSU5 Analog units  D-to-A converter is analog  Analog comparator for comparison of value to the input  These units are modeled in the testbench algorithmically

1/8/ L23 Project Step 9 - Sequential Machine Copyright Joanne DeGroat, ECE, OSU6 The digital portion  You are to model the digital portion  Inputs An over/under signal  a 1 indicates the value generated by the SAR is currently too high  A 0 indicates the value generated by the SAR is too low Start – begin a new conversion. The analog value has been captured. sarclk – the clock for the unit

1/8/ L23 Project Step 9 - Sequential Machine Copyright Joanne DeGroat, ECE, OSU7 The digital portion -2  The outputs eoc indicator signal line – indicates the end of the conversion and that the value on digital_val is valid digital_val – the 8-bit digital conversion value sar_val – an 8-bit output that is sent to the D-to-A converter internal to the entire unit  Note that part of the entire unit is modeled by the testbench. The assignment is only modeling of the controller, the digital portion.

1/8/ L23 Project Step 9 - Sequential Machine Copyright Joanne DeGroat, ECE, OSU8 Conversion basics  The input range is 0-5Volts  Starting state for converter state machine (1 st approximation) is or 2.5V  If this is less than input the next bit is set to 1, and again a comparison is made.  If this is greater than the input the bit is set 0 before the next bit position is set to 1,

1/8/ L23 Project Step 9 - Sequential Machine Copyright Joanne DeGroat, ECE, OSU9 Conversion example 1  Input 4.3 V  Start = 2.5 Under so keep  NS = 3.75 Under so keep  NS = Over so revert to 0  NS = Under so keep  NS = Under so keep  NS = Over so revert  NS = Under so keep  NS = Under so keep  Result is  EOC asserted

1/8/ L23 Project Step 9 - Sequential Machine Copyright Joanne DeGroat, ECE, OSU10 State machine  State machine has multiple states Ready to convert S1, S2, S3, S4, S5, S6, S7 while converting EOC – done converting

1/8/ L23 Project Step 9 - Sequential Machine Copyright Joanne DeGroat, ECE, OSU11 Notes on operation  Notes on operation Start will transition high when the analog input is valid and remains high during the conversion EOC is asserted and system asserting start will de-assert it Once start returns low, EOC is to be reset.  DO NOT SIMULATE UNTIL time’high TESTBENCH NEVER GOES QUIESENT Testbench has a free running clock, sarclk run 20 us instead

The Waveform 1/8/ L23 Project Step 9 - Sequential Machine Copyright Joanne DeGroat, ECE, OSU12