© 2008, Renesas Technology America, Inc., All Rights Reserved 1 Course Introduction Purpose  This course provides an overview of the Digital-to-Analog (D/A) converter (or simply, D/A) peripheral function that H8 series microcontrollers (MCUs) provide. Objectives  Understand the basics of D/A converters.  Discover key design facts about the D/A that H8 MCUs provide.  Gain insights about how to get the best performance from an on-chip D/A converter. Content  15 pages  3 questions Learning Time  25 minutes

© 2008, Renesas Technology America, Inc., All Rights Reserved 2 Digital-to-Analog Converters Typical Applications Digital servo tracking systems (~100Hz) Software programmable power supplies Simple sound generators (warning tones, etc.) Modem output circuits LCD contrast controls Text-to-speech outputs Alarm generators CPU D/A Converter Analog Voltage or Current

© 2008, Renesas Technology America, Inc., All Rights Reserved 3 Types of D/A Converters Two basic types: Low resolution (most common) Scaled Resistor Scaled Current Sources R-2R Ladder High resolution PWM types Scaled Resistor D/A Scaled Current Source

© 2008, Renesas Technology America, Inc., All Rights Reserved 4 R-2R Ladder Type D/A AVss DA Output AVref 1 Step3 Steps15 Steps255 Steps The number of output steps = 2n-1 where n is the number of bits.

© 2008, Renesas Technology America, Inc., All Rights Reserved 6 Typical H8 MCU D/A Converter DACR: D/A Control Register DADR0: D/A Data Register 0 DADR1: D/A Data Register 1 Control Circuit 8-bit D/A, 2 channels DADR1DADR1 DACRDACR Bus Interface Module Data Bus Internal Data Bus AVref AVCC AVSS DA0 DA1 DADR0DADR0 R-2R type Two separate converters 8-bit resolution Voltage reference (AVref) input is available so output value can be easily scaled. Module Stop

© 2008, Renesas Technology America, Inc., All Rights Reserved 7 D/A Control Register DAE: D/A Enable bit; enables the D/A converter. (This bit is shared by the two D/A channels; setting or clearing it affects both channels.) DAOE0, DAOE1: D/A Output Enable bits, one for each channel DACR Note: The D/A Control Register is set to the default state by either a Reset or by entering the Hardware Standby mode. Essentially, then, if you need to retain the analog output, use Software Standby mode. If you use Hardware Standby mode, you must re-initialize the D/A converter.

© 2008, Renesas Technology America, Inc., All Rights Reserved 8 Port Structure Transmission Gate Digital Buffer

© 2008, Renesas Technology America, Inc., All Rights Reserved 9 Basic CMOS Analog Switch Transmission Gate R ON R DS on

© 2008, Renesas Technology America, Inc., All Rights Reserved 11 H8S/2148A D/A Characteristics Condition A: Vcc and Avcc = 5.00V ±10%; AVref = 4.5V to Avcc Condition B: Vcc and Avcc = 4.5 to 5.5V; AVref = 4.0V to Avcc Condition C: Vcc and Avcc = 3.0 to 5.5V; AVref = 3.0V to Avcc

© 2008, Renesas Technology America, Inc., All Rights Reserved 12 D/A Conversion Time

© 2008, Renesas Technology America, Inc., All Rights Reserved 13 Filtering the D/A Output  This low-pass filter’s cut-off is about RC = 10 x 10 3 x = The cut-off frequency, F = 1/RC = 1kHz  In most cases, an active filter with better characteristics (such as a sharper roll-off, enhanced resistance to loading, etc.) is recommended at the output of the D/A.

© 2008, Renesas Technology America, Inc., All Rights Reserved 14 Maximum Output Frequency  Nyquist criteria: Must generate output samples at 2x the highest frequency of the waveform being recreated (This is the minimum requirement—a higher sample rate is better.)  Conversion time = 10µs (100kHz sample rate)  Therefore, the theoretical maximum output frequency = 50kHz  Problems/Limitations: - D/A conversions reduce CPU time available for other processing. (Typically, for an H8S/2148A, the highest frequency generated by the D/A will be less than 10kHz.) - If you sample at twice the frequency, you need a filter with a very sharp roll off. If you sample at higher rates, you can use simpler, less-expensive filters.

© 2008, Renesas Technology America, Inc., All Rights Reserved 16 Summary  Applications for D/A converters  D/A basics  Typical D/A performance