16-bits fixed-point PID implementations in C 1.0

The effect of fixed-point arithmetic in 16-bits PID controller C routineson the closed-loop precision is shown in this Simulink model.Two Simulink blocks that implement single and doubleprecision 16-bits PID C routines are generated with the LCT. The C sourcesare supplied for user modifications if required.Controllers work with 16-bits data and coefficients word lengths. Coefficientsand data fixed-point numbers have respectively 12-bits and 10-bits fractionnal part.For a reference step excitation, you will see that the permanent errors forthe fixed-point pids do not equal zero. Without rounding (look inside modelfor rounding mode switching), the single precision pid exibits an error about8 data lsb when the double precision one is just around 2 lsb.After changing the rounding mode to "nearest", the single precisionimplementation error falls to 3 lsb !Look inside the code sources and you will see that the differences are i) theinternal controller state is stored in double precision and ii) the downcasts(right shifts) are not done at the same point in the fixed-point computation.

Requirements:	No special requirements
Platforms:	Matlab
Keyword:	About8,  Double,  Downcastsright,  Equal,  Error,  Errors,  Excitation,  Exibits,  Forthe,  Inside,  Lsbafter,  Modelfor,  Permanent,  Rounding,  Shifts,  State,  Stored,  Switching
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