Motorola 68HC11 FAQ

HC11 analog module

What is the accuracy of the ADC?

+/-1LSB @ 2MHz

This assumes that Vdd is 5V. 1 LSB would be measured as
1/256 * Full Scale Voltage Reading (ideally, 5V),
which would be 0.01953V (19.5 mV).

Where can I read about the ADC module on the 6811s?

Chapter 12 of the Reference Manual provides an analog-to-digital explanation.

What is the fastest speed of acquisition for the ADC on the 6811 microcontroller?

It takes 32 E clock cycles for the Conversion Completion Flag (CCF) to set. Once the CCF flag is set, a complete conversion has taken place and the user program can read the result registers.

Application snapshots/notes:  AN-997

What design considerations should I take when using the ADC?

Voltage references should be extremely clean. Any voltage fluctuation can cause the ADC to give the wrong digital value. The 6811's environment must be protected from Electromagnetic interference.

How can I get rid of unwanted noise in my ADC reference pins?

1. Improve supply line decoupling to eliminate any high frequency noise which may be coming out of the microcontroller. The recommended decoupling capacitor size for single- chip applications is 0.1 microfarads.

2. Printed Circuit Board layout is important. For ADC input lines that are placed close to digital lines, noise is coupled inducing ADC errors, therefore, it is recommended to route ADC lines and Digital lines a part from each other.

3. Avoid operating the ADC in the internal RC clock mode if possible, especially in expanded mode. In RC clock mode, the ADC is running asynchronously to the rest of the processor, eventually causing sensitivity window to overlap a period of bus activity noise.

4. For best results, run the microcontroller in single chip mode.

Where in the acquisition sequence is the ADC most sensitive to noise?

The highest susceptibility of the converter to supply noise occurs in the last 30 nanoseconds (approximately) in the sample period ( 6 microseconds) of a conversion, which takes 16 microseconds at a 2.1 MHz bus frequency. Any disturbance to the ADC during this 30 nanosecond "window" is capable of causing an error. The most common source that disturbs the ADC are: supply noise generated internally by output buffers switching capacitive loads, especially in expanded/multiplexed operating mode. Decoupling for expanded mode is recommended and a capacitance should be applied at 1uFd paralleled with .01ufd. In single mode 0.1uFd is sufficient.

How does a heavy switching application environment affect my accuracy?

Unfortunately, heavy switching will affect the voltage reference applied to the ADC, and accuracy and precision of the ADC module are a function of the reference voltage. proper decoupling is recommended.

HC11 config module

How do I program the CONFIG register on 6811s?

The CONFIG register can be programmed in all MODES. The CONFIG register consists of and EEPROM byte and static latches that control the startup configuration of the MCU. The contents of the EEPROM byte are transferred into working latches during reset. In normal modes, changes to the CONFIG register do not affect operation of the MCU until the part is subjected to a RESET sequence. For a specific family of microcontrollers their CONFIG register programming routines are found in the Technical Data Documentation. The part number is MC68HC11X/D. Where X represents the family series.

For more documentation on the subject the following links are provided.

Application snapshots/notes:  AS-79 AS-104 AS-105 AN-997   

With what tools can I program the CONFIG register?

The CONFIG register can be programmed with the SPGMR11 under PROG11. Or one can build a circuit placing the 6811 in bootstrap mode and use PCBUG11 to program the CONFIG register. One can find the circuit for bootstrap mode in appendix A of the PCBUG11 Manual or construct a circuit where MODA and MODB are tied to ground and IRQ, XIRQ, and RESET are pulled up through a 4.7K Ohm resistor. Transmit and Receive on the MCU must go through an RS232 Level shifter. The part number for the Motorola level shifter is MC145407. Please refer to the data sheet for more information. With PCBUG11 and Bootstrap mode on the 6811, getting to know the part is easy and inexpensive.

Application snapshots/notes:  AS-104   AS-105   AN-997   

How does the NOSEC bit work on the 6811 Family?

In order for the NOSEC bit to work on 6811 family of microcontrollers, the nomenclature on the micro must specify that the feature has been enabled. This option does not come enabled on all members of the family. It is recommended to contact the sales office for more information.

Application snapshots/notes:  AS-104   AS-105   AN-997   

HC11 eeprom module

Where can I find the routines/algorithms to program the EEPROM/EPROM?

The algorithms are found in Technical summaries for each individual device.

What is the maximum amount of writes for the EEPROM?

Guaranteed to 10000 writes and 10 years data retention.

What is the time required to Erase the EEPROM on a 711E9 devices?

The typical time for a bulk erase is 10 ms.

Can I use the so called PROG mode on 6811s?

NO. Motorola discourages customers from using this mode.

If you purchase a programmer you should find out if the programmer uses the bootstrap mode to program the microcontrollers.

Are there any relevant Application Notes/Snap Shots on this subject

Yes, The following documents have information on programming the EEPROM using different tools.

Application snapshots/notes:  AS-16_Programming_EPROM_and_EEPROM_on_the_M68HC11EVM  





What can I do to protect the integrity of data residing on EEPROM module?

The biggest enemy of an EEPROM cell is the introduction of a transient that violates the electrical specification of the microcontroller. A transient in the negative domain can cause damage to the cell to the point of rendering the cell useless.

HC11 gpt module

How can I generate a software delay with an Output Compare?

By enabling an Output Compare and each time the program
executes the interrupt handler and offset value is added to
TCNT and stored to the respective TOCX.

Are there any documents on PWMs with HC11s?


Application snapshots/notes:  AS-25_(PWM_tutorial_for_K,KA,KW,P_and_PH_series)  

HC11 modes module

Where do I find a typical schematics for the 6811 in bootstrapmode?

The typical circuit can found on the PCBUG11 Manual in appendix A.
However, to setup up the part in its simplest form MODA/B are tied
to ground, IRQ and XIRQ are pulled up throuh a 4.7kOhm resistors.

HC11 pwm module

How can I generate a software delay with an Output Compare?

By enabling an Output Compare and each time the program
executes the interrupt handler and offset value is added to
TCNT and stored to the respective TOCX.

Are there any documents on PWMs with HC11s?


Application snapshots/notes:  AS-25_(PWM_tutorial_for_K,KA,KW,P_and_PH_series)  

HC11 reset module

Should I meet the RESET requirements for RESET and POR on the 6811/12 families?

A microcontroller is a highly sensitive state table the at reset expects a set of signal conditions as an input to get into the correct mode of execution. These conditions are based on RESET MODA and MODB if the timing on these conditions are not met properly because of random spikes either below or above the rails the following symtoms will be experienced when running your application:

1. EEPROM corruption either bit or byte.
2. Incorrect execution of the program.
3. I /O pins will not read the proper expected conditions.

What design considerations should one take when designing with 6811s?

1. Make sure the Vdd, MODA, and MODB have achieved their proper logical levels at the time the microcontroller releases RESET. The processor will release reset after seeing 4064 E clock cycles. Should the processor release RESET before these signals are stable the micro will not RESET as desired. For timing specifications please refer to M68HC11RM/D. There is one parameter not defined that is the time for Reset to transition from low to high.

2. Make sure that your PCB layout allows configuration of MODA and MODB.

3. Make sure that RESET has a 4.7k Ohms pullup and that no capacitance is used between RESET and the ground plane.

Are there any other documents pertaining to HC11 reset issues?


Application snapshots/notes:  AS-8_(How_to_Configure_HC11_Reset_Pin)