Cypress makes our standard USB controller, the AN2131SC. The specifications of this microcontroller are provided in Table , and its data sheet can be downloaded from the Web at www.cypress.com/cfuploads/ img/products/AN2131SC.pdf.
As can be seen from here, besides the USB microcontroller the USB connector is the second special component of the basic circuit.
There are two versions, called ‘Type A’ and ‘Type B’. The Type A version is always located on the PC or hub side, while the Type B version is always found in the peripheral device that logs in to the PC. Power can be drawn from a Type A connector, while a Type B connector can receive power. Consequently, we use exclusively Type B connectors (Figure) in our circuit. A USB cable is always wired 1:1. A maximum of 500 mA can be drawn via the USB cable, but the Cypress IC must first report this level of current consumption, since if the PC does not have this much reserve power capacity it will automatically switch off the device. The AN2131SC IC automatically reports a value of 100 mA via its internal USB communications software. If the hardware needs more current, you must write your own software for USB communications.
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USB connector pin assignments
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HW design
By the FT232BM datasheet and well known R232 - TTL converter MAX232 I managed to design following circuits, which scheme can be seen below:
Unlike a recommendation mentioned in FT232BM datasheet I missed EPROM where identification information concerning USB device can be stored like VID, information concerning power consumption etc. The circuit will work even without EPROM. USB cable with ferrite bead should be connected on JP1 pins. In most cases the USB cables have following colour scheme:
Unlike a recommendation mentioned in FT232BM datasheet I missed EPROM where identification information concerning USB device can be stored like VID, information concerning power consumption etc. The circuit will work even without EPROM. USB cable with ferrite bead should be connected on JP1 pins. In most cases the USB cables have following colour scheme:
PIN | Colour | Meaning | JP1 |
1 | +5V | 1 | |
2 | DATA minus | 2 | |
3 | DATA plus | 3 | |
4 | GND | 4 |
There are two kinds of USB connectors: A and B. Type B can be avaliable in USB B mini variant as well. On the picture bellow there are A and B connectors.
Easiest way to get USB cable is to buy one in special computer shop as cable for reduction between A and B kind of connector or cable for USB port extension. Then we can cut the cable and use the part with A connector only. Mentioned cables are usually without the ferrite bead, however even without ferrite bead it works well.
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