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README: replace obsolete hardware description with the hardware history

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Werner Almesberger 2013-02-04 19:33:17 -03:00
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@ -12,17 +12,35 @@ and to examine possible integration into future devices.
This work is licensed under the terms detailed in the file COPYING. This work is licensed under the terms detailed in the file COPYING.
Hardware architecture Hardware history
--------------------- ----------------
IEEE 802.15.4 transceiver chips are available from several manufacturers, IEEE 802.15.4 transceiver chips are available from several manufacturers,
including Atmel, Freescale, and Texas Instruments. These chips are similar including Atmel, Freescale, and Texas Instruments. These chips are similar
in size, functionality, and cost. The first prototype is based on the in size, functionality, and cost. The first prototype of this project was
Atmel AT86RF230. based on the Atmel AT86RF230.
The RF module will be physically placed on the left side of the LCD The initial plan was to place the RF module on the left side of the LCD
module, replacing part of the display's PCB. module of the Ben NanoNote, replacing part of the display's PCB. When
installed in the Ben, the transceiver would connect directly via SPI to
the Jz4720. For development, a SiLabs C8051F326 microcontroller
implemented a USB to SPI conversion.
When installed in the Ben, the transceiver will connect directly via SPI Then Rikard Lindstrom came up with the idea of using the Ben's 8:10 card
to the Jz4720. For development, a SiLabs C8051F326 microcontroller slot as a general expansion interface, which led to the idea of making
implements a USB to SPI conversion. a WPAN card in that form factor, with the benefit of being readily usable
with any Ben already in existence.
Thus the project was split in two parts: the atben card that had only the
transceiver chip and would be used with the Ben, and the atusb card that
would be similar to the original design but abandoned its clear physical
separation of USB and RF.
Meanwhile, an improved version of the AT86RF230, the AT86RF231, became
available and the designs were updated for it. It also turned out that
the clock from the Ben was too noisy to be used as a clock source for
the transceiver. Therefore, a crystal was added to the atben design.
Finally, the SiLabs C8051F326 was replaced by an ATmega32U2, mainly
because the latter has a larger Flash memory and greater community
acceptance.