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Appendix A: QScreen Electrical Specifications

General Specifications

The QScreen Controller combines an embedded computer based on the 68HC11 microcontroller with a touch panel and LCD (liquid crystal display) graphic user interface (GUI) that is ideal for instrument control and automation.



Motorola 68HC11F1 microcontroller with 16 MHz clock speed and 4 MHz bus speed. Paged memory expands the processor’s address space to 8 Megabytes.



3 or 4 input capture functions facilitate accurate detection of pulse edges and measurement of pulse widths with a resolution of 2μs.

4 or 5 output compare functions make it easy to create complex waveforms and pulse-width modulated signals up to 20KHz at 50% CPU load.

A pulse accumulator facilitates frequency measurement and pulse counting up to 2MHz.



21 interrupts support the 68HC11’s on-chip subsystems.


Runtime security

A watchdog timer and clock monitor ensures orderly reset after an error.


Touchscreen/display user interface

High contrast CCFL white-on-blue monochrome LCD display with software controlled backlight.

4.8" diagonal (4.25" x 2.25"), 240 x 128 pixel display.

5 column by 4 row touchscreen with software controlled beeper for audible feedback. Custom antiglare, clear, and EMI touchscreens are also available for quantity orders.

Optional intrinsic safety barrier on touchscreen.



A hardware UART supports either RS232 or RS485 at up to 19.2 Kbaud.

A second software UART implements RS232 at up to 4800 baud.

A fast synchronous serial peripheral interface (SPI) provides communications at speeds up to 2 megabaud.



Your QScreen includes a high-efficiency switching regulator with surge suppression, transient filtering, and EMI/RFI filtering to provide clean supplies for the onboard analog and digital electronics. You need only supply regulated or unregulated DC power in the range of 8 to 26 volts.

Surge Suppression

The raw input is protected by a "varistor" rated at 33 Volts DC. This metal oxide surge suppresser protects a Qscreen by clamping high voltage spikes before they have a chance to do any harm. The varistor has no effect if the input voltage is less than the maximum specified, or 26 volts. Above 33 volts the device starts to conduct current, and it acts like a short circuit to high voltages, thus clamping the voltage spikes. To prevent this varistor from consuming current, you should make sure that the maximum DC voltage supplied is always less than 26 volts.

EMI/RFI filter

Additional protection is provided by an electro-magnetic interference (EMI) and radio frequency interference (RFI) filter that prevents high frequency noise from invading the circuitry via the power input, and also prevents EMI from propagating back to the external power supply. The EMI filter is implemented by a two stage PI network of inductors and capacitors. The output of the first stage filter, called V+raw, is passed to the Wildcard module bus for supply to Wildcard modules that require their own unregulated DC power. This unregulated voltage is free of high-frequency and high-voltage transients. If you design custom add-on Wildcard boards, we recommend that you use V+raw as the input for local 5 Volt regulators. It is good design practice to place local voltage regulators on each board, as this minimizes noise problems and improves modularity.

The QScreen Controller is designed for reliable low noise operation. It is implemented as a state of the art 6-layer surface-mount board. Two inner layers are dedicated ground and power planes, providing low-impedance return paths for digital current spikes.

Parameter Min Typ. Max Units Conditions
Input Voltage 8 26 Volts
Power Usage 3.5 Watts No Wildcards
Power Usage – per Wildcard 0.5 Each Wildcard

Operating conditions

Parameter Min Max Units Conditions
Operating Temperature Range – Electronics 0 70 °C Industrial Temp also available
(-40 to 85°C)
Operating Temperature Range – Monochrome Display -20 60 °C
Storage Temperature Range – Monochrome Display -20 70
Humidity 0 95 % Relative Humidity At 0 to 45°C, no condensation
Humidity 0 85 % Relative Humidity At 50°C, limited by the monochrome display. At other temperatures the absolute humidity must be less than that provided by 85% RH at 50°C, or 100% at 47°C.


Parameter Standard With Option Units
Flash 512 1024 KBytes
RAM 513 KBytes
EEPROM 512 Bytes
Compact Flash Wildcard 64-2048 MBytes

CPU I/O (CPU Ports A, D, E)

Parameter Min Max Units Conditions
I/O Voltage Range -0.1 5.3 Volts
Input Low Voltage 1.0 Volts 0.2 x VDD
Input High Voltage 3.5 Volts 0.7 x VDD
Input Leakage Current ±1 μA
Output Low Voltage 0.4 Volts at 1.6 mA
Output High Voltage 3.7 Volts at –0.8 mA and VDD=4.5 V
Output Source 25 mA <65 Ω output drive impedance, one pin at a time, observing max power dissipation limits.
Output Sink 25 mA <65 Ω output drive impedance, one pin at a time, observing max power dissipation limits.
Note: We recommend limiting total package power dissipation accruing from I/O current to 800 mW or less, to assure that the junction temperature remains below 125ºC.

8-bit analog to digital (A/D) conversion

Parameter Min Typical Max Units Conditions
Number of Input Channels 8
Sampling Frequency 100,000 Samples per second
Input Voltage Range -0.1 0.0 to 5.0 5.1 Volts
Nonlinearity 1 LSB
Absolute Accuracy 2 LSB
This page is about: QScreen Controller IO Summary, Memory Description, Freescale 68HC11 IO Summary, 8-bit ATD Conversion – QScreen Controller electrical specifications, memory description, and input-output (I-O) summary