Universal Serial Bus Hardware - The Options
When someone says USB Microcontroller, Cypress normally springs to everyone’s mind. No wonder when Cypress has an extensive range of USB Microcontrollers in both 1.5Mbps & 12Mbps versions. On top of this, they have the popular USB Starter Kit (CY3640) for $99 US. However life is not this simple. What Cypress omits, is their Kit comes with no code for the host application and more importantly, the host driver.
I have heard that Cypress do not plan to make another run of their windowed CY7C63001A. Should you be after a replacement, Cypress is offering a tube of OTP’s as compensation. Better make sure your code is perfect. You only have approximately 25 goes at it!
CY7C63001
Should you wish to extend to higher speed devices, Cypress’s High Speed USB MCU’s requires specialised programmers and development tools that come at great cost. Cypress is a good start, should your company desire to sink a bit of money for some nice toys.
Motorola has had since 1997, the 68HC705JB2, a 20 pin Low Speed USB MCU based on their popular HC05 Core. However since late 1997, I’ve been trying to source them. . . . Some distributors have a small quantity (5-10) of the OTP parts, but this is not much good if you can’t source a windowed device for development. Too bad they are Obsolete now. I may try for some 68HC705JB3 / JB4's now . . .
68HC705JB2 Obsolete / Discontinued
Motorola have just recently extended their MCU range to include a JB3 & JB4.
These are again low speed devices coming in a 20 or 28 pin package. These are
prequalified parts and Motorola should start production of these IC’s any day
now. (April/May 1999).
68HC705JB3 68HC705JB4
Philips has a nice alternative - A add on full speed USB Device. The problem with low speed USB Devices, is the restriction of transfer modes. A full speed device can use Isochronous, Control, Interrupt or Bulk transfer modes. A low speed device is restricted to Control & Interrupt Modes. Therefore by Philip's making their Serial USB Device Full Speed, even though the I2C interface is limited to 2Mbps, the designer has the added flexibility of all transfer modes.
Other added advantages are - why waste time learning a new architecture? With the USB Interface I.C.’s you can use your existing designs, existing code and existing development tools. All you need to do is modify the design to hang the USB Device of the bus. What could be cheaper? These devices are popular with PIC die hards, as Microchip currently doesn’t have a USB MCU. I'm told things will be changing with the introduction of the PIC18CXXX family, however.
PDIUSBD11 - USB Interface Device with Serial Interface
PDIUSBD12 - USB Interface Device with Parallel Bus
There are disadvantages to these devices, namely board real estate. You wouldn’t make a USB Mouse with these chips. However both come in surface mount devices giving a very small footprint. They are also not intended for self powered devices.
I’m finding the Philip's I.C.’s difficult to source. Some of these manufacturers should look at Maxim’s Small Credit Card Order Facilities. On other thoughts, maybe we should encourage Maxim to make a USB Serial Interface Engine!
Philips also has a USB Transceiver Chip, the PDIUSBP11. This I.C. will convert USB into a Digital CMOS Serial stream. Couple this with a Xilinx FPGA or Altera PLD and write your own Serial Interface Engine.
PDIUSBP11 - Universal Serial Bus transceiver
National Semiconductor has done the same thing with their USBN9602 8 bit Parallel or Microwire USB Device. National Semiconductor has combined both a Serial and Parallel Version into the one I.C., which makes sense when it comes to needing to stock only the one I.C.
The biggest problem with these is it’s 48Mhz Oscillator. The Philip's devices used a PLL to generate the 48Mhz internal Clock. The result, a cheap 6 or 12Mhz Crystal can be used. (Also have to remember, EMC regulations)
USBN9602 USB Full Speed
National Semiconductors devices are normally easier to obtain than Philip’s, making this option more attractive if you are having trouble sourcing Philip’s ICs.
| Universal Serial Bus Information | Steve Lawther details some more USB MCU's and devices. |
| USB Webboard | Ask for Help, or have you say with the USB Webboard. |
| USB Designer Links | Quite a comprehensive page of links to manufacturers and products. Great starting point to see what is out there. |