topic Re: Any 8 Bit Freelance Coders + USB Device Driver in 8-bit Microcontrollers

Any 8 Bit Freelance Coders + USB Device Driver

Sparks — Sat, 29 May 2010 23:17:42 GMT

HI Guys

If this is in the wrong place then please let me know and I will move it/ correct it.

I am looking to locate a freelance coder for development of 8 bit products (freescale) and I currently use the MC908JB16DWE but that isn't restrictive at all and able to look at other Freescale product options.

Services required would be device programming for development of USB peripherals, for which I would provide the PCB design and proto boards to work with.

Ideally someone with USB device production/programming experience, and knowledge and experience of device drivers would be a total asset.

Will mainly be involved in switch monitoring projects - possibly some motor drives and solenoid drives, and optical chopper disk monitoring for trackballs/ spinners etc

Thanks in advance

Jeff F

Re: Any 8 Bit Freelance Coders + USB Device Driver

Tsuneo — Sun, 30 May 2010 13:54:07 GMT

Services required would be device programming for development of USB peripherals, for which I would provide the PCB design and proto boards to work with.

I don't apply to your project, but just advice.

I've seen many troubles caused by this development role assignment.

USB application requires specific consideration for board design.The points are twofold,

1) Bus- or Self- powered -- VBUS detection

2) Noise -- isolation

1) Bus- or Self-powered -- VBUS detection

The type of power supply is determined by supposed operation of your device, not by the amount of current which the device draws from USB.
- Bus-powered

The device works just when it connects to a host

- Self-powered

The device works in stand alone, too.

For Bus-powered device,

The MCU is supplied by USB. USB line provides power supply capacity of 100mA or 500mA, depending on the host side. When power requirement of your device exceeds these capacity, you will have an extra power supply to satisfy the requirement. But in this case also, the MCU is still supplied by USB. The extra power supply for peripherals is switched by the VBUS (5V supply) pin on the USB connector.

For Self-powered device,

The MCU has to know physical connection of USB. As MC908JB16 doesn't have specific pin for VBUS detection, you have to assign a spare port pin for this purpose. This port pin connects to VBUS pin on the USB connector, across a protection resistor, with another weak pull-down resistor, and a small bypass capacitor.

In this topic, we discussed on self-powered configuration.

https://community.freescale.com/thread/64806

2) Noise -- isolation

Noise affects to the oscillation of the on-chip OSC. It causes missing or extra clock. USB-PHY (decoder/encoder) on MCU is more sensitive to clock disorder than MCU core. Even when the MCU core seems to run without trouble, USB communication is disturbed.

Motor/solenoid drive often causes heavy noise issue.You may need to isolate signal/control GND from power GND.

- Isolated power supply for the MCU

- Optical coupler for output port

- Ferrite beads for input ports of external sensor connection.

Hope this post will help you,

Tsuneo

Re: Any 8 Bit Freelance Coders + USB Device Driver

Sparks — Sun, 30 May 2010 16:11:44 GMT

Hi Tsuneo

Thanks for your comments

I have a few BUS powered products finished already and I have done some research with the self-powered limitations of the USB bus as per your notes - I have kept those considerations in mind when calculating overall power consumption of the circuit in its entirity (down to individual pullup resistor values - lol)

Initially the devices in the range will be self-powered and then I will move up to more demanding PCBs in terms of power supply requirements for motors and other driver type devices, where the integration of different supplies on one board will lead to noise suppression requirements being more strictly implemented.

Your points on the isolation methods are spot on and they are some of the techniques that will be implemented by the hardware designer, which I will also assist with in terms of PCB design/layout (taking into consideration PCB trace runs also )

Thanks again

Jeff F

Re: Any 8 Bit Freelance Coders + USB Device Driver

Tsuneo — Sun, 30 May 2010 20:07:49 GMT

Initially the devices in the range will be self-powered and then I will move up to more demanding PCBs in terms of power supply requirements for motors and other driver type devices, where the integration of different supplies on one board will lead to noise suppression requirements being more strictly implemented.

You are still trapped in the wrong idea widely spreads over, that requirement of device power supply determines Self- or Bus- powered. Required power supply of the entire device is not the primary criteria. Supposed operation, works in stand alone or not, is the primary one.

- Even when the device requires 100A, the USB MCU is configured as bus-powered, if the device works only with USB connection, not stand-alone. The power-hungry peripherals are supplied with a separate source, which interlocks to VBUS voltage.

- Even when the device draws just 2.5 mA from USB line, it is a self-powered device when it works in stand-alone, too. This device requires VBUS detection.

Tsuneo