1998-04-06 , ESC-9745

Philips Semiconductors offers lower system cost solutions for USB peripherals

Philips Semiconductors has devised the 'FlexiUSB'architecture for medium to high-end USB hub applications, so that microcontrollers do not have to be integrated into the hub IC. This flexible, modular approach results in a lower overall system cost, shorter development time and faster time-to-market.

The FlexiUSB architecture is built into the company's new range of USB hub and interface ICs, comprising the  PDIUSBH11A,  PDIUSBH12,  PDIUSBD11 and  PDIUSBD12. These new devices provide an easy way to add USB capabilities to existing product designs that use interfaces such as RS232, parallel and SCSI.

The key to this new architecture is reducing the amount of microcontroller bandwidth required by the hub IC. This is done by storing the commands in a buffer on the hub IC and sending these out to the microcontroller when it can accept them. If the buffer is full, because the microcontroller has not had time to upload the instructions, the hub IC rejects any new packets. The USB automatically keeps trying to re-send the packet until it can be accepted into the buffer. This means that the bandwidth requirements and the power demand on the microcontroller are kept to a minimum, and can be handled when the microcontroller is not busy. Without this approach of constricting the bandwidth, more powerful or dedicated microprocessors would be required to respond instantly to requests by the hub ICs.

As a result, any microcontroller can be used in conjunction with the FlexiUSB hub IC. This is very important for creating medium and high-end USB peripherals, which are likely to have been already created using a particular microcontroller. The alternative solutions are to change the existing microcontroller and lose all the investment in existing software, or to have two microcontrollers: one for the hub that may be integrated on the hub IC and one for the application. Both result in higher system-build costs than Philips Semiconductors' solution which only uses a small part of the existing microcontroller.

For example, adapting a P/S2 keyboard with a built-in touch pad to become a USB device is simply a matter of adding one of Philips SemiconductorsÌ new FlexiUSB hub ICs. The existing investment in the software for the keyboardÌs microcontroller is retained, because the microcontroller stays the same. The small additional load on the microcontroller is estimated to be around 1%.

Another factor contributing to the lower system-build cost of this approach is that integrating a complex microcontroller into a USB hub IC requires a package with a large number of pins. These packages are much more expensive to produce than having the microcontroller and hub IC in two separate, smaller, standard packages. Apart from the cost aspect, it is also much easier to design with this approach because the microcontroller is a standard product and is fully supported with software libraries and established design and debug tools. This gives a lower design risk, greater flexibility and faster time-to-market for the final device.

An example of this flexibility - which can only be achieved with the FlexiUSB architecture - is when designing for the Advanced Configuration and Power Interface (ACPI), where it is much easier to work with two chips. The hub IC monitors for any wake up instruction which is passed to the microcontroller to bring it out of sleep mode. Doing this in a single integrated chip, i.e. without FlexiUSB, would be more complex and require more power.

This new family provides complete systems solutions across the range for customers' USB hub needs at the lowest cost implementation. FlexiUSB covers the medium- to high-end applications and is complemented by Philips Semiconductors' leading position in stand-alone, 80C51-based microcontrollers. The PDIUSBD11 and PDIUSBD12 provide just USB functionality while the PDIUSBH12 gives the additional support of two USB ports; the PDIUSBH11A supports four ports. For low-end keyboards, monitors, etc., where there is not much difference in the two approaches, Philips Semiconductors also provides USB hubs ICs (the P8xCx9x series) with simple integrated microcontrollers so that customers have a choice of solutions.

Philips Semiconductors, a division of Philips Electronics NV, headquartered in Eindhoven, The Netherlands, is the ninth largest semiconductor supplier in the world. Philips Semiconductors' innovations in digital audio, video, and mobile technology position the company as a leader in the consumer, multimedia and wireless communications markets. Sales offices are located in all major markets around the world, and are supported by regional customer application labs.