Question 1

ADUC834: What is the minimum time (or ADC cycles) to get a reading if the input is a step?

Accepted Answer

Q 
 What is the minimum time (or ADC cycles) to get a reading if the input is a step? 
 
 A 
 Often confusing for our customers, because of the chopping scheme we use, the full settling time through the ADC is 2 x tadc (see page 28 in the ADuC834 datasheet). This means that the time taken to a first conversion result is twice the throughput time. This also means that if you change (or step) the input then you will have to wait 2 full conversion times to see a valid output or more correctly put is the settling time to an asynchronous step input will not be reflected on the output until the third subsequent output ( because the step change could happen in the middle of a current update cycle and you have to wait 2 FULL cycles to see the settled result, result in 3 cycles in total.

Question 2

ADUC834: What's the difference between the INL spec and the noise spec on the ADC?

Accepted Answer

Q 
 What's the difference between the INL spec and the noise spec on the ADC? 
 
 A 
 Any given ADC conversion result has both an INL error and a noise error. The INL specification is 15ppm of FSR max (i.e. the INL error at any given code is accurate to at least 16 bits). Depending on the range and the update rate this ADC conversion result will have a varying amount of noise on it. The noise which exists on this ADC conversion result is random and is equally as likely to be positive as negative. Hence by doing more averaging this noise error can be reduced. Since the INL will stay constant for every ADC conversion (given the same DC input) then software averaging will not remove the INL error.

Question 3

ADUC834: What is lowest power consumption configuration for 10 hour sample conversion intervals?

Accepted Answer

Q 
 I just want to initiate a sample conversion every 10 hours, what is my lowest power consumption configuration in this mode? 
 
 A 
 The ADuC834 can be programmed into power down mode by setting PCON.1. This powers the whole chip down into a low power mode. The Time Interval Counter (TIC) on the ADuC834 is the only peripheral which can remain powered up while the chip is powered down. The TIC allows you to wake the chip up from powerdown mode every particular interval. Therefore if you only wish to initiate a sample conversion every 10 hours the chip can be left in power down mode for the 10 hours. Once the 10 hours has elapsed the chip will wake itself up allowing you to perform an ADC conversion, wait for the result, and the go back to power down mode. In this mode the average current will typically be about 8uA for a 3V supply.

Question 4

ADUC834: What external clocks can be used? Can the PLL be bypassed?

Accepted Answer

Q 
 What external clocks can be used with the ADuC834? Can the PLL be bypassed? 
 
 A 
 The PLL circuit on the ADuC834 will lock to 384 times the input clock as long as the clock frequency is within the frequency range 32.768kHz &plusmn; 20%. The ADC incorporates 50Hz and 60Hz rejection filters which assume a 32.768kHz input frequency. Using an input clock that differs from 32.768kHz will cause these rejection filters to move. Although it is possible to use the ADuC834 with an input clock other than 32.768kHz it is recommended that you use a 32.768kHz clock/crystal to preserve the ADC functionality. There is no mode of operation on the ADuC834 that allows the PLL to be bypassed. Hence the ADuC834 cannot be driven directly with an oscillator other than 32.768kHz +/-20%.

Question 5

ADUC834: What baud rates can be achieved?

Accepted Answer

Q 
 What baud rates can be achieved by the ADuC834? Can the ADuC834 achieve a baud rate of 115200 baud when used with a standard 32.768kHz watch crystal. How is this done? 
 
 A 
 The ADuC834 can achieve baud rates up to 393kbaud. In terms of standard baud rates the highest baud rate obtainable by the ADuC834 is 230400 baud. Yes, the ADuC834 can achieve a baud rate of 115200 when used with a standard 32.768kHz watch crystal. The ADuC834 includes a special baud rate timer that allows much more flexibility as regards achieving particular baud rates (see page 63 of the datasheet for more details). There are two advantages why one should configure the baud rate using the UartBaud generator. 1) To achieve particular standard baud rates up to and including 115200 and 230400 baud. 2) To free up a timer. The user is free to use all 3 timers for timer functions while the baud rate is controlled via the UartBaud generator.

Question 6

ADUC834: What are the implications of having unbuffered differential reference inputs?

Accepted Answer

Q 
 What are the implications of having unbuffered differential reference inputs? 
 
 A 
 The unbuffered reference input provides a high impedance, dynamic load. Because the input impedance of each reference input is dynamic, resistor/capacitor combinations on these inputs can cause dc gain errors depending on the output impedance of the source that is driving the reference inputs. Reference voltage sources, like those recommended (AD780) will typically have low output impedances and therefore decoupling capacitors on the REFIN(+) and REFIN(-) inputs would be recommended. Driving the reference input voltage across an external resistor, as in many ratiometric configurations, will mean that the reference input sees a significant external source impedance. External decoupling on the REFIN(+) and REFIN(-) pins would not be recommended in this type of circuit configuration.

Question 7

ADuC834: Values of the internal pull up resistor

Accepted Answer

Q 
 There is everywhere in the manual that port's have pull-up's, but what are the values of the pull-up's in ports 1, 2 and 3 ? 
 
 A 
 You can optimise the value of the pull ups depending on the speed and power requirements. 10kOhms is a good start. The maximum value is determined by the leakage current and the noise margin to the positive rail or the maximum risetime required combined with the line capacitance. 10kOhm usually satisfies both of these requirements.

Question 8

ADUC834: Use of PSEN pin on Microcontroller v 8051

Accepted Answer

Q 
 The PSEN pin is always an output on an 8051. How then can it be used as an input to enter serial download mode? What pulldown resistor should be used to be sure to enter serial download mode? Is the standard functionality of the PSEN pin affected? 
 
 A 
 On an 8051 the PSEN pin is always an output. It is used to access external code memory. On the Microcontroller the PSEN pin is used to access external code memory and is used as an input to determine whether to run user code or run the on chip serial downloader. The PSEN pin is normally configured as an output. When the RESET pin is pulled high, the PSEN pin becomes a digital input and the voltage at the PSEN pin is sampled every machine cycle. Once the RESET pin is released (low) the last sampled logic level of the PSEN pin is used to decide whether to run from user code or whether to run the on chip serial downloader. To ensure that the PSEN pin is interpreted as a logic low it should be pulled low through a 1k resistor to ground. To ensure that the PSEN pin is interpreted as a logic high it can be left float as there is an internal pullup resistor. Because the functionality of the PSEN pin on the ADUC8xx Microcontroller only differs from that of an 8051 when RESET is pulled high (in this condition the PSEN pin on an 8051 is useless) the functionality of the PSEN pin on the ADUC8xx Microcontroller is unaffected by its additional functionality.

Question 9

ADUC834: The reference input is differential. Can I use a single ended reference?

Accepted Answer

Q 
 The reference input is differential. Can I use a single ended reference? 
 
 A 
 Yes, REFIN- can be grounded if a single ended reference is being used.

Question 10

ADUC834: Should I use the internal voltage reference or an external voltage reference?

Accepted Answer

Q 
 The ADuC834 features an internal voltage reference but I have been recommended to use an external voltage reference. Is this correct? If so why is the internal reference present? 
 
 A 
 Yes, we do recommend that an external voltage reference is used for the applications that require good ADC accuracy. Typically the internal voltage reference is only 13-14 bit accurate and will not be useful for most applications. The WASP (available as part of the QuickStart? Development System) allows you to compare the noise performance of the ADuC834 with an internal and an external voltage reference. The internal voltage reference is often used with the auxiliary ADC where the very high accuracy might not be required. Often the primary ADC is used with a ratiometric voltage reference which will be useless for another measurement. In this case the internal reference can be used for the second measurement. The internal voltage reference is also necessary for the internal temperature sensor.

Question 11

ADUC834: Overwriting the ADC factory calibration coefficients

Accepted Answer

Q 
 I want to overwrite the ADC factory calibration coefficients. Do I have to do a calibration every time I run my software. 
 
 A 
 Every time the ADuC834 is reset, the factory calibrated calibration coefficients are downloaded to the calibration registers in the SFR space. Hence these SFRs must be overwritten with your individual calibration coefficients. To avoid having to do a calibration every time that the ADuC834 powers up it is often easier to write the calibration coefficients to the Flash/EE data memory space. Then in your own initialization the coefficients can simply be read from the flash/EE data memory and the calibration process does not have to be repeated.

Question 12

ADUC834: Minimum and maximum external voltage references allowed by the ADuC834.

Accepted Answer

Q 
 What are the minimum and maximum external voltage references allowed by the ADuC834. 
 
 A 
 The minimum voltage reference allowed between REFIN+ and REFIN- is 1V. The maximum voltage reference is AVDD.

Question 13

ADUC834: Is it possible to switch OFF the internal buffer of primary ADC?

Accepted Answer

Q 
 Is it possible to switch OFF the internal buffer of primary ADC? Some of the AD77xx family have this particular feature on board. Can I turn chopping off like on AD77xx parts so as to increase throughput time? 
 
 A 
 No, it is not possible to turn off the internal buffer of the primary ADC. The auxiliary ADC provides an unbuffered input if required. It is also not possible to turn ADC chopping off on the ADuC834.

Question 14

ADUC834: Why does ADC effective resolution depend on range and update rate

Accepted Answer

Q 
 The ADC noise tables on page 30 of the ADuC834 datasheet show that the effective resolution depends on the range and update rate selected. Why? 
 
 A 
 The ADuC834 features Sigma Delta ADCs. Sigma Delta ADCs use a method of averaging (using a sinc3 filter) to obtain the very high accuracy ADC conversion results. The more averaging that is done the more accurate the ADC conversion is going to be. With high update rates the ADC gets to perform less averaging in hardware on the chip. Hence the resolution will not be as good. With slower update rates more averaging is done on the chip and the resolution is improved. The resolution of the ADC also depends on the input voltage range. Noise added to an input signal with the ADC converting on the 2.56V range will affect the conversion result much less (128 times less) than the same amount of noise being added to a signal converting on the 20mV range. Hence converting on a larger signal will produce an ADC result accurate to many more bits.

Question 15

ADUC834: Is it possible to accidently write to security bits and prevent part entering download mode?

Accepted Answer

Q 
 The ADuC834 features security bits to restrict access to Flash/EE code and data space. Can I accidentally write to them in my code and prevent the part from entering serial download mode? 
 
 A 
 The ADuC834 facilitates three modes of Flash/EE program memory security. These modes can be independently activated, giving different levels of security to your code as described in the ADuC834 datasheet (pg 38) The security bits are read-only from user code and exist at byte address FFFEh. They can be read using the following piece of code. MOV EADRH, #0FFh ; address the Sec Bits page MOV EADRL, #0FEh MOV ECON, #81H ; read byte command The security bits can be only be set after parallel programming the ADuC834 or directly after a serial download by following the serial download protocol as described in AN-1074. This protocol is implemented in our Windows serial downloader (WSD) available as part of the QuickStart development system.

Question 16

ADuC834: Interfacing the ADuC834 to a RTD

Accepted Answer

Q 
 I've got two questions: 1. Is there any performance difference between old RTD connection (in ADuC824 datasheet with ref resistor connected to EXC) and new RTD connection (in ADuC834 datasheet with ref resistor connected to AGND)? 2. Can I connect two RTDs serially (4 way connection each) and measure their resistance on AIN1-2 and AIN3-4? What would be suggested decoupling (if any)? 
 
 A 
 There is no performance difference between the two implementations. The circuit shown on the ADuC834 datasheet is advantageous as it uses one less resistor. The key requirements are: Maximize the full-scale voltage drop across the RTD to maximize resolution Keep the total voltage drop across the sense resistors and RTD within the voltage compliance range of the current source (VDD-0.6V) And ensure you meet the input common mode requirements of the ADC input (AGND+100mV to VDD-100mV). Yes it is possible to use multiple RTDs with the same current source (in series). Again, simply ensure you meet the voltage compliance range of the current source and the input range of the ADC. Decoupling requirements will depend on how harsh an environement the RTD are placed in. If the RTDs are on the same board as the ADuC, not exposed to noise and the ADuC power supply is well decoupled, you probably will not require any decoupling capacitors on the analog inputs. However, if the RTDs are located remotely via long cables in an electrically harsh environment (lots of magnetic field and EMI) you will need to look at adding capacitors to filter the spurious signals. 10nF would be a good starting point but I suspect a little trial and error coupled with a reasonable estimate of the likely interference / noise signals will provide the best solution.

Question 17

ADUC834: Impact of fast logic edges on analog performance

Accepted Answer

Q 
 I have some fast logic edges on some of the digital circuitry I plan to connect to the MicroConverter. Will these signals impact the analog performance of the chip? 
 
 A 
 Signals with rise and fall times of less than 5ns or so, when applied directly to a MicroConverter&rsquo;s digital input pins, can potentially feed through and degrade analog performance. A simple solution to this problem is found in the form of a series resistor. A series resistor of around 200&Omega; will slow an edge sufficiently that it won&rsquo;t affect the MicroConverter&rsquo;s analog performance.

Question 18

ADUC834: I want to initiate the serial downloader through the SPI port, how can I do this?

Accepted Answer

Q 
 I want to initiate the serial downloader through the SPI port, how can I do this? 
 
 A 
 A bootloader mode is implemented on the ADuC834 allowing re-programming of the flash/EE program memory using any peripherals or any protocol that the user wishes. To download to this space you will have to write your own downloader in the 6kBytes of bootloader space (E000H -> F7FFh of flash/EE program memory) to download to the rest of the flash/EE program memory. The downloader can use any means to download, parallel, SPI, I2C, UART or any other protocol you wish.

Question 19

ADUC834: I am changing ranges and I am seeing much more than 2uV gain mis-match. Why?

Accepted Answer

Q 
 ADuC834: I am changing ranges and I am seeing much more than 2uV gain mis-match. Why? 
 
 A 
 You should not see much more than 2uV gain matching. i.e. as you changes the range from one range to another the difference in an ADC results between one range and the next should typically correspond to less than 2uV. However if you have performed a system offset calibration then you will have changed the offset calibration registers (OF0H/M/L). Since the ADCs use chopping there is no need for an offset calibrated in the factory. Hence the default offset calibration coefficients are 800000h. Once a system offset calibration is performed the OF0H/M/L get overwritten by values that when subtracted with a zero input will produce a zero reading. When the range is changed, however, the offset calibration registers still apply to the previous range. e.g. if on the 20mV range a system offset of 10uV existed producing an offset calibration coefficient of 802100h. Now imagine that the range is changed to the 40mV range. The OF0L register still reads 802100h. This corresponds to an offset of 20uV on the 40mV range. On the 2.56V range the offset would correspond to 1.28mV. There are two ways to prevent large offset gain errors from occurring when the ranges are changed. The first way is to calibrate the system offset at each of the ranges, and store the different calibration results into flash/EE data memory. Then whenever the gain is changed the appropriate calibration coefficients can be downloaded from flash/EE data memory. The second way is to calibrate the offset at the 20mV range. Then whenever you change the range you should appropriately change the OF0H/M/L SFRs so that the difference between OF0H/M/L and 800000h is halved every time the range is increased one level as shown in the following expression: OF0H/M/Lnew range = 800000h + (OF0H/M/L20mV range &ndash; 800000h) / 2^RN

Question 20

ADUC834: How do I use the on-chip temperature sensor feature of the ADuC834?

Accepted Answer

Q 
 How do I use the on-chip temperature sensor feature of the ADuC834? 
 
 A 
 The temperature sensor on the ADuC834 is converted by the auxiliary ADC to output a digital code to represent the chip temperature. The auxiliary ADC must be configured in bipolar mode using the internal voltage reference in order for the temperature sensor to produce sensible results. The temperature sensor is calibrated in the factory at 25&deg;C so that the ADC conversion result is 8000h at 0&deg;C with 256 counts per &deg;C. e.g. An ADC conversion result of 9680h represents a temperature of 22.5&deg;C. An ADC conversion result of 6756h represents a temperature of &ndash;24.66&deg;C. And remember, the on-chip temperature sensor is measuring chip temperature, not ambient temperature, so don&rsquo;t forget to factor self-heating into the equation if you wish to determine the temperature of the ambient air.

Popular Forums

Product Forums

Application Forums

Design Center Forums

Highlighted Webinar

Places

Libraries

Latest Webinars

Challenge Yourself!

What's Brewing

Places

Resources

Highlighted Blogs

Latest Blogs

ADI Blogs

Visit ContentZone

Featured Content

View Content By Industry

View Content By Technology

ADUC834: FAQ