AN1740 Freescale Semiconductor / Motorola, AN1740 Datasheet
AN1740
Related parts for AN1740
AN1740 Summary of contents
Page 1
... Motorola, Inc., 1998 For More Information On This Product, A pair of voltage comparators Input channel multiplexer (MUX) A current source A temperature sensing diode Associated control bits and flags AN1740 Go to: www.freescale.com Order this document by AN1740/D AN1740 ...
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... Analog subsystem overview Voltage comparators Current source/discharge Analog signal multiplexers Support circuitry Analog power-up considerations Analog-to-digital (A/D) conversion Pitfalls in using single slope A/D Manual A/D conversions Automated A/D conversions General A/D techniques Design check list For More Information On This Product, Go to: www.freescale.com AN1740 MOTOROLA ...
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... Discharge Device A discharge device is also attached to the constant current source output. Either the current source is ON, the discharge device is ON, or both are OFF. This allows control of an external charge storage device, AN1740 MOTOROLA For More Information On This Product, Two voltage comparators A constant current source supply voltage ...
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... EPROM versions or is specified as a mask option on the ROM versions Analog MUX register (AMUX) at $0003 Analog control register (ACR) at $001D Analog status register (ASR) at $001E For More Information On This Product, Go to: www.freescale.com AN1740 MOTOROLA ...
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... TCAP PORTB LOGIC PB4 AN4 TCMP MUX4 V AOFF + V – SS (VREF) • (MUX1) • (MUX2) • (MUX3) • (MUX4) Figure 1. Analog Subsystem Block Diagram AN1740 MOTOROLA For More Information On This Product CHG CHARGE CURRENT CONTROL LOGIC CP2EN + COMP2 – (HOLD) • (DHOLD) ...
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... MUX3 MUX2 PDIB4 PDIB3 PDIB2 PDIB1 IEDG ICEN CPIE CP2EN CP1EN 0 CMP2 VOFF* COE1* * Controlled by mask option. AN1740 MOTOROLA Bit 0 PB0 MUX1 PDIB0 OLVL 0 Bit 8 Bit 0 Bit 8 Bit 0 ISEN CMP1 ...
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... CPFR1. Therefore, the CPF1 bit can be used to capture events when the comparator’s positive input was above its negative input. Comparator 1, therefore, permits software subroutines to either poll the AN1740 MOTOROLA For More Information On This Product, Table 1 Table 1 ...
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... This essentially creates an adjustable threshold for resetting the MCU or causing an IRQ interrupt. Possible uses would be low battery detection, level alarms, and low-voltage reset. If the comparator 1 output drives the IRQ function, the additional IRQ source can be made 8 Figure 3. For More Information On This Product, Go to: www.freescale.com AN1740 MOTOROLA ...
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... In this case important that the PB2 and PB3 pins are configured as inputs with their pulldowns disabled. AN1740 MOTOROLA For More Information On This Product, supply voltage. In this case important that the ...
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... V DD CP1EN PB2 COMP1 R – PB3 CPFR1 INV OPT PB4 COE1 OLVL = 0 PB4 = 0 CASE CP1EN PB2 COMP1 R – PB3 CPFR1 INV PB2 INPUT DDRB2 PB3 INPUT DDRB3 CASE 4 Q CPF1 R CMP1 CASE 5 MOTOROLA CPF1 CMP1 CPF1 CMP1 AN1740 ...
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... The divider nominally divides the input by 2 which allows the selected PB1:PB4 pin to be tied to a voltage level activate the divider, the DHOLD MUX must be enabled. AN1740 MOTOROLA For More Information On This Product, Its output can be monitored by the dynamic output SS ...
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... CAN ALSO USE PB2, PB3, OR PB4 WITH REQUIRED MUX For More Information On This Product, Go to: www.freescale.com CPF2 C R CPFR2 CMP2 CASE CPF2 C R CPFR2 CMP2 CASE CPF2 C R CPFR2 CMP2 DATA DDRXX = 1 CASE 5 AN1740 MOTOROLA ...
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... REF CAN ALSO USE PB2, PB3, OR PB4 WITH REQUIRED MUX V PB0 X DIODE = (HOLD) • (DHOLD REF V Y Figure 5. Additional Comparator 2 Configurations AN1740 MOTOROLA For More Information On This Product, MUX1 CP2EN COMP2 – DHOLD INV 60 k SAMPLE CAP (10 PF) CP2EN ...
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... shown in Figure 6, when the – 1.5 volts For More Information On This Product, Go to: www.freescale.com ensure DD level DD . For DD level is at 5.0 volts, DD falls to 4.29 volts, the upper DD falls farther, the input can DD approaches the minimum DD AN1740 MOTOROLA ...
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... Basic comparators like this can have input voltage offsets millivolts. This amount of offset can be significant, especially when monitoring signals near V below V change state and the comparator will look “stuck” even though both AN1740 MOTOROLA For More Information On This Product, and always keep one input to the voltage DD 6 ...
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... INPUTS EQUAL – B — INITIAL INPUT OFFSET NEGATIVE can effectively change. Since the input offset is P For More Information On This Product, Go to: www.freescale.com . The input SS . Thus Thus, IO – IDEAL COMPARATOR + X – + – – Figure MOTOROLA AN1740 ...
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... However invert, the sense of the comparator is inverted using the INV bit, then V positive input of the comparator. The 10-mV input offset is still with respect to the internal negative input, but now is “moved” to the external V so that: P AN1740 MOTOROLA For More Information On This Product, Figure 8 where above V N ...
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... INV = Table For More Information On This Product, Go to: www.freescale.com as given in Table 2. Polarity of input offset (see Figure 7) Case A, positive Case B, negative – The inputs can both be tied recommended MOTOROLA AN1740 ...
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... DHOLD bit in the AMUX register. The last three sources ( all can be controlled by the AN1740 MOTOROLA For More Information On This Product (equivalent of 2 volts) ...
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... B. This is accomplished by writing logical 1s to the desired PDIB bits in the PDRB at location $0011. 20 DIVIDED 100 FREQUENCY – HZ Figure 9. Typical Channel AC Input Impedance For More Information On This Product, Go to: www.freescale.com DIRECT 100 K AN1740 MOTOROLA 1 M ...
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... The dynamic output bits merely follow the state of the output of each comparator. There is no timing synchronization in passing the state of the CMP1 and CMP2 bits to the ASR. The dynamic output bits are useful AN1740 MOTOROLA For More Information On This Product, The static flags, CPF1 and CPF2 The dynamic outputs, CMP1 and CMP2 Go to: www ...
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... OPT mask output option, compare MOR or ROM level, OLVL Timer OLVL state For More Information On This Product, Go to: www.freescale.com Table 3. Comparator 1 Comparator 1 output output, CMP1 enable, COE1 CMP state AN1740 MOTOROLA ...
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... CPU bus cycles as follows: • • Software polling should not be used for pulses separated by less than 30 CPU bus cycles. AN1740 MOTOROLA For More Information On This Product, 21 cycles to acknowledge; max instruction plus stacking Six cycles to clear the static flag (BSET) 19 cycles to return; RTI plus unstacking ...
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... Discharge source device CHG X OFF 0 OFF 1 ON Figure For More Information On This Product, Go to: www.freescale.com Action Current source and discharge OFF device both disabled ON Discharge current into PB0 OFF Source current from PB0 1, the current source, discharge to 4 volts. SS MOTOROLA AN1740 ...
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... A whenever the ISEN bit is set, even if the PB0 pin is not sourcing current and the discharge device is active. As the voltage on PB0 changes, non-linearity creates up to about 1% variation in the nominal 100- A source current. AN1740 MOTOROLA For More Information On This Product, change in the source current. ...
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... VOLTAGE ON PB0 – VOLTS Figure 10. Typical Current Source Behavior (PB0) Figure 11. For volts, the equivalent discharge DD For More Information On This Product, Go to: www.freescale.com MAX COMMON MODE RANGE The design goal was volts, the equivalent DD MOTOROLA 5 AN1740 ...
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... Freescale Semiconductor, Inc Current spikes can occur when discharging an external capacitor through PB0, which can be disruptive to the internal analog V respect to the external V AN1740 MOTOROLA For More Information On This Product VOLTAGE ON PB0 – VOLTS Figure 11. Typical Discharge Current Behavior (PB0) pin ...
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... The analog signal multiplexer is divided into two sections: • • 28 pin and cause unwanted analog noise. SS The channel select bus The comparator input bus For More Information On This Product, Go to: www.freescale.com SS Figure 12 controlled by AN1740 MOTOROLA ...
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... Therefore, the user must control the multiplexers in the proper sequence to avoid shorting two channels together during the transition. Unless the user has determined that switching transients are not a AN1740 MOTOROLA For More Information On This Product, TO COMPARATOR INPUT BUS (VREF) • ...
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... The normal mode is to have the HOLD bit , the divided input is needed by selecting the DD DD For More Information On This Product, Go to: www.freescale.com offset voltage SS Figure 13. to make REF – 3 volts and still not exceed the + 0.3 volts could DD AN1740 MOTOROLA DD ...
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... INTERNAL DIODE TEMPERATURE DIODE CHANNEL HOLD SELECT BUS 60 k DHOLD 60 k HOLD AN1740 MOTOROLA For More Information On This Product, (HOLD) • (DHOLD) COMPARATOR INPUT BUS (HOLD) • (DHOLD) SAMPLE CAP (10 PF) (HOLD) • (DHOLD) (HOLD) • (DHOLD) • (VOFF) 100 MV OFFSET – ...
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... PB3 to a voltage conversion resistor Figure volts. DD and dividing by two for two channels in parallel, dividing by Figure 15. In this example, two current sources, I For More Information On This Product, Go to: www.freescale.com 14. This impedance can volts and DD and I , are 1 2 AN1740 MOTOROLA ...
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... With this setup, the currents through port pins should be limited to less than 1 mA. AN1740 MOTOROLA For More Information On This Product ...
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... For More Information On This Product, Go to: www.freescale.com CHANNEL SELECT BUS MUX1 HOLD MUX2 MUX3 MUX4 OTHER CONNECTIONS TO PB1 THROUGH PB4 HAVE BEEN OMITTED FOR CLARITY Figure 16. As shown AN1740 MOTOROLA ) MUX3 OR ) MUX4 can ...
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... Avoid driving input pins below V OFF, as the input protection diodes will start turning on at about –0.3 volts and inject high currents through the V the input pins more than 0.3 volts above the V AN1740 MOTOROLA For More Information On This Product, , even if the channel multiplexers are ...
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... Figure 36 Figure 17 with typical input impedance as shown previously MUX 800–2900 MUX Figure 17. Divider Equivalent Circuit For More Information On This Product, Go to: www.freescale.com supply level HOLD 8–13 pF DHOLD AN1740 MOTOROLA ...
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... Therefore, if connected through the divider to the channel select bus, there should always be sufficient time to charge the sample capacitor (seven RC time constants or about six AN1740 MOTOROLA For More Information On This Product, Figure 9 ...
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... Another source of sample corruption comes from substrate current injection which can occur when the input protection diodes begin conduction in order to limit inputs which have gone above V 38 pin recommended that switching of any SS For More Information On This Product, Go to: www.freescale.com ground SS or below DD AN1740 MOTOROLA ...
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... AMUX register, there can occur some charge redistribution due to the tiny variations in delays between all the multiplexers. The only exception to this is when AN1740 MOTOROLA For More Information On This Product low voltage input creates the most sensitivity SS ground bounce noise ...
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... ISEN, CP1E, or the CP2E bits in the ACR order to flip the comparator output Figure 18. current is drawn when the VOFF bit is set, and DD For More Information On This Product, Go to: www.freescale.com . Otherwise, SS level, the magnitude and phase SS line. The sampling SS , and the SS AN1740 MOTOROLA . SS ...
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... HOLD and DHOLD bits are set. For this supplied, the general analog bias source must be powered up. This can be done by setting either the ISEN, CP1E, or CP2E bits in the ACR. Once powered, the diode’s voltage will change approximately 2 mV/ C. AN1740 MOTOROLA For More Information On This Product, CP2EN ...
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... When the pulldown for PB0 is on when charging an external capacitor, the ramp will look like an RC charge curve rather than a linear ramp. 42 Figure 19. For More Information On This Product, Go to: www.freescale.com AN1740 MOTOROLA ...
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... The ICF, OCF, and TOF timer flags interact to start and stop the current source driving PB0. Under this control, the ICF has priority over both the OCF and TOF. Further, the latched static flag, CPF2, of comparator 2 is AN1740 MOTOROLA For More Information On This Product, ...
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... Always clear the ICF flag following any change in the state of the ICEN, ICIE, and IEDG bits. without any enabling control. They can get set before the software is ready to use them. For More Information On This Product, Go to: www.freescale.com AN1740 MOTOROLA ...
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... Analog-to-digital (A/D) conversion can be accomplished using the JJ/JP series by allowing the current source to charge up (ramp) an integration capacitor connected to PB0 and using comparator 2 to detect the time when the ramp voltage crosses the unknown voltage being measured as shown in AN1740 MOTOROLA For More Information On This Product, Figure 20. ...
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... A/D and require its own D/A conversion circuitry Some “filtering” of input signal provided by the integration Inherently monotonic bits are possible with long conversion times For More Information On This Product, Go to: www.freescale.com V DD OFF V CAP PB0 AN0 I DISCHG ON + CMP2 V X PBX – DISCHARGE (CHG = 0) DISCHARGE AN1740 MOTOROLA ...
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... CHG where: t CHG EXT I CHG AN1740 MOTOROLA For More Information On This Product, Slow conversion times, in the milliseconds More software required to do the actual conversion External ramp capacitor needed C EXT ------------------------------ - I CHG = Charge time (seconds) = Voltage to reach (volts) ...
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... C EXT f OSC CHG C EXT = -------------------------------------------- - f OSC EXT OSC -------------------------------------------------------- - P I CHG . Since the charge current Usually, the clock frequency is fixed by other OSC For More Information On This Product, Go to: www.freescale.com fixed at 100 A, the only CHG MOTOROLA , AN1740 ...
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... Using core timer P Using 16-bit programmable timer Using software loops Clock source frequency (excluding any prescaling Vdc OSC Vdc DD 1. Limited for less than 2.0 F. EXT AN1740 MOTOROLA For More Information On This Product, Min — 1.0 1.1 0.032 0.128 0.512 2 ...
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... Min and max full scale voltage (volts) MAX ,f = Min and max oscillator frequency (Hz) MAX , I = Min and max charge current ( A) MAX = Prescaler selected (count/count sure to include any effects caused by expected OSC For More Information On This Product, Go to: www.freescale.com , C , and I . OSC EXT CHG , V , EXT FS AN1740 MOTOROLA ...
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... When the ramp capacitor is fully discharged, go back to step 3. Refer to application note A/D Conversion Software for the MC68HC05JJ/JP Series Microcontrollers , Motorola document order number AN1739/D, for detailed software examples on how to implement a mode A/D conversion. AN1740 MOTOROLA For More Information On This Product, Go to: www.freescale.com Application Note ...
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... Therefore, the input above the maximum conversion level, the conversion can be terminated, and the conversion result can be forced to its maximum value. 52 Infinite conversion time Disabled conversions Extra conversions Early conversions Conversion overlap Conversion masking 21. For More Information On This Product, Go to: www.freescale.com AN1740 MOTOROLA ...
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... However, in this case, the ramp voltage does indeed reach the input level, but the CPF2 flag is not set because conversion did not discharge PB0 low enough to make CMP2 go low again. This is referred to also as the “stuck at zero” condition. This is shown in input offset case. AN1740 MOTOROLA For More Information On This Product ...
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... Typical MC69HC05JJ/JP series MCUs tend to have the channel could be used to determine which SS Comparator Inversion For More Information On This Product, Go to: www.freescale.com – IDEAL COMPARATOR + – + – V – CONVERSION CHANGE FALSE FLAG MODE 2 OR MODE 3 ONLY as shown in Figure 22. A page 16. MOTOROLA CMP2 AN1740 ...
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... These captured times appear like completed conversions with unexpected timing. Therefore, the A/D conversion software should clear out any extra CPF2 flags before starting another conversion. AN1740 MOTOROLA For More Information On This Product, V ...
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... Figure 24. In this case, the polarity of the comparator’s input ICF Figure 24. Early Conversion A/D Fault For More Information On This Product, Go to: www.freescale.com . A good rule of thumb SS NOISE EXPECTED SPIKE TRIP MODE 2 OR MODE 3 ONLY MODE 2 OR MODE 3 ONLY AN1740 MOTOROLA ...
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... The problem of conversion overlaps can be detected if one or more software flags are present so that the TOF or OCF interrupt routine can determine that a prior conversion has been started but not finished. Two suggested software flags are: • AN1740 MOTOROLA For More Information On This Product ...
Page 58
... V 58 EOC — End of conversion – Set when ICF detected at end of conversion – Clear when TOF or OCF occurs starting charge cycle Figure 26. This ICF cannot be evaluated until after the . SS For More Information On This Product, Go to: www.freescale.com . This SS AN1740 MOTOROLA ...
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... Timing Via Timer Timing of the conversion can be done by reading the state of the 16-bit Reads timer or the multifunction timer. The software must account for the delays in reading these registers and the asychronous clocking of these AN1740 MOTOROLA For More Information On This Product ...
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... CPF2 flag check at one-half of a “bit time” for proper rounding of partial bits. The details of these two examples are given in the two following software examples, and the timing is shown in 60 For More Information On This Product, Go to: www.freescale.com Figure 27. Figure 28. AN1740 MOTOROLA ...
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... AN1738/D , for additional information on the exact cycle when hardware changes and/or reads occur in the JJ/JP-series microcontrollers. This application note also shows how to measure these timings in other MC68HC05 Family members. AN1740 MOTOROLA For More Information On This Product, Go to: www.freescale.com Application Note ...
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... DISABLE INTERRUPTS CLEAR ACCUMULATOR SET CHG BIT IN ACR TO START RAMP DONE INCREMENT ACCUMULATOR TIMING DELAY OVERFLOW? For More Information On This Product, Go to: www.freescale.com ATDGO2 ADD INITIAL TIME DELAY ATDLP IS YES DONE CPF2 FLAG SET? NO ADD CYCLE YES COUNT FAULT NO MOTOROLA AN1740 ...
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... FAULT 33 0812 DONE AN1740 MOTOROLA For More Information On This Product, org $0800 CPFR2,ASR sei clra bset CHG,ACR brset CPF2,ASR,DONE inca bra ATDLP * org $0800 CPFR2,ASR sei ...
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... ATDGO1 — MODE 0 A/D CONVERSION WITHOUT DELAYS IDEAL 1/2 BIT TIME 14 CYCLES R BRSET CPF2 ADD NOP NOP ATDGO2 — MODE 0 A/D CONVERSION WITH DELAYS For More Information On This Product, Go to: www.freescale.com 11 CYCLES R BRSET CPF2 INCA BRA ATDLP R BCC BRSET CPF2 ADD NOP ATDLP AN1740 MOTOROLA ...
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... The TOF flag bit is set whenever the 16-bit timer counter overflows 2. The OCF flag bit is set whenever the 16-bit timer counter matches 3. The ICF flag bit is set whenever an input capture is received by the AN1740 MOTOROLA For More Information On This Product, from $FFFF to $0000 regardless of whether or not the timer overflow interrupt is enabled (TOIE bit set in TCR) ...
Page 66
... IEDG bit in the TCR. e. The trigger source for the ICF can be either the signal on PB3 or the output of voltage comparator 2 dependent on the state of the ICEN bit in the ACR. For More Information On This Product, Go to: www.freescale.com 57 and 58. These flags AN1740 MOTOROLA ...
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... ATD1 and ATD2 bits as required. Refer to application note A/D Conversion Software for the MC68HC05JJ/JP Series Microcontrollers , Motorola document order number AN1739/D, for detailed software examples on how to implement a mode 2 or mode 3 A/D conversion. AN1740 MOTOROLA For More Information On This Product, Go to: www.freescale.com Application Note ...
Page 68
... In mode 2, the triggering event is the TOF. If the OCF is not being used for some other task, it can be used to trigger the start of the sample just before the next TOF occurs. Then in the TOF service routine, the sample 68 For More Information On This Product, Go to: www.freescale.com AN1740 MOTOROLA ...
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... REF V OFF OFF N REF This calculation also is shown as a flowchart for both absolute and ratiometric values in AN1740 MOTOROLA For More Information On This Product OFF – REF V OFF + --------------------------------------- - N REF N OFF – = Calculated value of measured voltage (volts) = Value of known reference voltage (volts) ...
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... Go to: www.freescale.com SUBTRACT 2V FROM 2V SS REF SAVE RESULT AS 2V REF SUBTRACT 2V FROM SAVE RESULT DIVIDE 2V FROM 2V IN REF MULTIPLY RESULT BY ASSUMED VALUE FOR REF SS DIVIDE RESULT BY 2 SAVE RESULT CONVERTED VALUE OF UNKNOWN VOLTAGE STORED AN1740 MOTOROLA ...
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... The voltage drop due to the resistance of a package lead is minor compared to the inductance of the lead, which is particularly a problem with fast switching currents. AN1740 MOTOROLA For More Information On This Product, lines are connected to the V ...
Page 72
... Transients with low frequency components, therefore, always will affect all readings in a similar manner. internal MCU bus activity has been halted. For More Information On This Product, Go to: www.freescale.com with AN1740 MOTOROLA ...
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... An advantage of wait mode is the reduction of digital switching noise as previously discussed. This makes wait mode a good candidate for taking “low noise” readings with the analog subsystem. AN1740 MOTOROLA For More Information On This Product, Analog Subsystem Low-Power Modes current will exist ...
Page 74
... PB4 using the OPT mask option and the COE1 bit in the ASR. Then PB4 is connected externally to an IRQ pin or the RESET pin. NOTE: Comparator 1 can be used to control an external signal using the COE1 function, even if the device is in stop mode. 74 For More Information On This Product, Go to: www.freescale.com AN1740 MOTOROLA ...
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... All A/D modes A/D converters. Use a proper type of capacitor for the external ramp capacitor to avoid problems All A/D modes with linearity on long conversion times. AN1740 MOTOROLA For More Information On This Product, contains a listing of major considerations for each feature of the Table 7. Design Checklist Design consideration Go to: www ...
Page 76
... VOFF or COE1 functions are required. 76 Design consideration after the HOLD and DHOLD bits have REF For More Information On This Product, Go to: www.freescale.com Refer to page number 44 71- 22, 40 AN1740 MOTOROLA ...
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... Oxford University Press, New York, N.Y., 1987, ISBN 0-19-510720-9. Guinta, Steve, “Capacitance and Capacitors,” Analog Dialogue 30-2 , Analog Devices, Inc., 1996. Kester, Walter, “A Grounding Philosophy for Mixed-Signal Systems,” Electronic Design , Analog Applications Issue, June 23, 1997. AN1740 MOTOROLA For More Information On This Product, Go to: www.freescale.com Application Note ...
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... Freescale Semiconductor, Inc. Application Note 78 For More Information On This Product, Go to: www.freescale.com AN1740 MOTOROLA ...
Page 79
... Freescale Semiconductor, Inc. AN1740 MOTOROLA For More Information On This Product, Go to: www.freescale.com Application Note References 79 ...
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... Mfax™, Motorola Fax Back System: RMFAX0@email.sps.mot.com; http://sps.motorola.com/mfax/; TOUCHTONE, 1-602-244-6609; US and Canada ONLY, 1-800-774-1848 HOME PAGE: http://motorola.com/sps/ are registered trademarks of Motorola, Inc. Motorola, Inc Equal Opportunity/Affirmative Action Employer. For More Information On This Product, Go to: www.freescale.com Mfax is a trademark of Motorola, Inc. © Motorola, Inc., 1998 AN1740/D ...