better by design...

What does Microbus Better by Design mean?
At the start of any embedded-PC development, the first choices made in component selection and choices in design affect the total cost of ownership of any system based around it. It affects the long term supply, the EMC performance, the EMC costs, the practical reliability and choices for self-protection and recovery.

As OEMs buy in more integrated technology, Microbus designs reflect the quality-based choices that the OEM would have made where a small increase in component costs will give a long term benefit.

Long term supply
Microbus' focus is design and manufacture of the latest technology, with a commitment to maintain long-term supply products. For example. Microbus still manufacture 486 cards, first made 8 years ago, and Pentium cards made 5 years ago. Microbus offer long term supply to support the OEM's cost of ownership. Unlike the desktop PC market, where it is very easy to see a $1 component reduction quickly saving hundreds of thousands of dollars, there is not the same service, quality of manufacture, test requirements or expected long term product performance. Direct costs to an OEM include service, re-qualification and test. Therefore you quickly see that Far Eastern product is only designed to reduce the prime costs. Microbus is fully aware of long term costs, re-qualification, retest, re-certification and aim to reduce the overall cost of ownership for OEMs.

EMC
Many of the EMC design practices adopted by Microbus have been established over years of use in medical, military and other applications historically requiring strict EMC performance. With the market having an ever increasing focus on EMC performance and requirements for strict adherence to standards such as FCC and CE, Microbus's established practices can save integration costs and should ease the development of EMC compliant systems. Long term supply again reduces costs for the re-testing of systems.

While selection of the best components for EMC suppression, combined with careful design and layout can have an impact by increasing direct material costs, the return is in the overall system costs. The ceramic capacitor is a very good EMC de-coupling device and is readily used in Microbus designs. Cheaper components do not have the same characteristics. Different parts of the circuits require different selection of capacitors. Where others would use Aluminium Electrolytic, Microbus chooses to use Tantalum. While the Aluminium Electrolytic would survive a warranty period, the long term operation does not match Tantalum.

For power supply design we use OS-Con or PosCaps. Again, in preference to the Aluminium Electrolytics. With many voltage levels used within the boards, careful design and de-couplings of the ground planes are required. This can include additional PCB layers to achieve the best EMC performance.

Microbus backplanes or direct power supply connections include filtered 5V and grounds, again preventing noise to and from the power supply.

Defining 5V only boards helps in PSU design as well as EMC. The serial channels, using converted 5V do not output the same levels of noise to that of a 12V serial.

Watchdogs
The software watchdog allows programs to use BIOS calls to pulse the watchdog I/O port. If the watchdog does not receive a pulse in a suitable time, it raises an external alarm and resets the system. This can be used to guard against application code leaving the system hanging. A voltage watchdog holds the card in reset if the voltage falls out of specification, to rule out the risk of erroneous operation and ensure reliable processing of data.

Backplane design
The outer layers of backplanes are used for separate +5V and 0V, and all signals have a ground interleave. Power line filtering and Resistor-Capacitor (RC) termination is provided. These practices reduce problems of noise, cross talk and ringing, and maintain signal integrity across the bus.

Batteries
Cards include a battery built into a Dallas Real Time Clock/CMOS device, or a high-capacity UL-certified lithium battery, used in designs that support non volatile SRAM disks. If an external battery is connected, the board uses the better voltage supply.

Reliability
The reliability of a board can be considered in two ways: calculated component-based MTBF and practical reliability.

MTBF
Microbus supply calculated MTBF details from the manufacturing database and can be supplied for any assembly. Samples of these calculations are included in each manual with a description of the BT HRD4 MTBF background.

Similar designs will broadly produce the same calculated MTBF details, as it is usually a matter of presentation and temperature assumptions that can differentiate. The BT HRD4 assumes an operating environment of 55°C without the usual calculated benefit of every 10° lower, doubling the MTBF. You may see other manufacturers' MTBFs calculated to 20°C for example. By adding additional protection and EMC precautions to our designs we actually reduce the MTBF (though by a very small amount), but improve the practical reliability and EMC performance massively.

practical reliability

ESD
Microbus are aware that our SBCs have passed extremely high levels of simulated electromagnetic pulses where others have failed. The specification of the highest level ESD protection on the RS232/485 are an example of intention of long term operation. These specify +/-15KV protection on the human body model, +/-8KV for IEC 1000-4-2 contact discharge, and to +/- 15KV for IEC 1000-4-2 air gap discharge.

External power protection
Where power is taken off the board, self healing fuses are provided. The fuses protect external shorts from damaging the board, but also self-heal, removing the requirement to replace the board once the external short has been removed.

Keyboard, mouse and USB are protected by 0.5 amp self-healing fuses, the power connection to a flat panel, and SCSI termination have 1 amp protection. It may be worth noting that VGA, serial and parallel interfaces are not designed to distribute power.

Reduced handling
The more a board is handled, the more likely it is that a fault will be introduced. Microbus' boards are designed without jumpers to reduce handling requirements. All hardware settings can be set up in the CMOS, and can be backed up in the EEPROM.

The serial number and board type can be read in the software, removing the requirement to open a system, or alternatively, could be remotely interrogated.

Controlled configuration of CMOS
By programming the EEPROM, customers have a reliable way to frequently define the CMOS. For scheduled orders, these can be set at Microbus at no extra charge. This configuration method also supports automatic recovery of corrupt CMOS's and is an easy method for field service personnel to recover customer defaults should any unauthorised person adjust the setting. *Note: that there is also an option to stop people entering the CMOS setup.

The EEPROM is also used to define how the system boots dependent upon defined error status. For example, keyboard error can be PC standard "display error and pause", alternatively "display error and continue" or "ignore". These options can be selected for 14 different test conditions. The Power On/Self Test status can also be displayed on the screen during boot. Since this detail is stored in the EEPROM, and is an extension to standard PC design, it is immune to battery problems. Boards can be used without a battery, restoring defaults from the EEPROM. In this mode, date and time are not maintained.

Fans
As x86 processors developed, power consumption increased, and the Pentium® class processor introduced a requirement for fans. Microbus strive to enable the OEM to limit the opportunity for fans to cause reliability issues. Included in all fan selection criteria is 5V operation, with direct connection to the board to save accidental cable damage. Rotational speed monitoring is another feature common to all Microbus boards. This, coupled with the ability to monitor the CPU temperature, and being able to throttle back the processor speed when necessary, allows the OEM to incorporate monitoring to prevent degradation of the fan and causing a total system failure.