A couple of days ago, Ron pointed me to some new WLAN chip/module solution: https://www.gainspan.com/products/GS1011MIC_modules.php
Since it's not clear where this chip is an improvement over the things we already looked at (with non-public documentation and other troublesome issues), I suggested he check whether the data sheet is complete. For example, this is what complete data sheets look like: [1] http://www.atmel.com/dyn/resources/prod_documents/doc8111.pdf [2] http://focus.ti.com/lit/ds/symlink/cc2520.pdf [3] http://www.atmel.com/dyn/resources/prod_documents/doc8271.pdf [4] http://www.diodes.com/datasheets/74AHC1G00.pdf This information can also be split into several documents, e.g., a hardware description and a programming manual. To make things a little more difficult, many companies also publish summary or "short" data sheets. They're good enough to get a first impression of the chip in question, but they lack the information necessary to actually use it, e.g., to write a driver for it. Sometimes, the "short" data sheets also lack electrical information. Examples of short/incomplete data sheets: [5] http://www.atmel.com/dyn/resources/prod_documents/8271S.pdf [6] http://www.sige.com/files/DST-00405_SiGe_SE2436L_Datasheet_Rev_1_0_SF_Jan-10-2011%20(1pager).pdf As the example of the ATmega48/... shows, the mere existence of a short data sheet doesn't mean that there's no full data sheet, but we can't take it for granted (without seeing it) either. A good indication for a first estimate is the size. A full data sheet of even very simple chips (e.g., [4]) is rarely shorter than five pages. If the chip talks to a microcontroller, expect tens of pages. If it contains a CPU of some kind, the documentation is usually larger than 100 pages. A complete data sheet has the following content. I'm giving the page numbers in the AT86RF231 data sheet [3] as a reference: - brief functional overview (page 1), - pin assignment (page 2) and pin description (pages 3-4), - example circuit, often called "application circuit" (most but not all data sheets have this. Can be in a separate document. Pages 12-15. Many data sheets don't explain the circuit.) - electrical characteristics, such as maximum voltages (usually under "absolute maximum ratings"), supply voltage, etc. (page 156) - detailed voltage, current, and timing data for all the types if pins (pages 157-161) - package drawing (can be in a companion document; page 174) The above elements are present in all complete data sheets, even for components as simple as an 74AHC1G00 gate [4]. Components that talk to a microcontroller will also have the following information. Again, with page numbers from the AT86RF231 [3]: - description of the physical protocol spoken with the host, at the bit level (this is sometimes left out or kept very short if the protocol is complex and clearly standardized/described elsewhere, e.g., USB or MMC/SD/SDIO; pages 16-18) - description of the content carried by the physical protocol, e.g., a "write register" command. Some of the (useless) "short data sheets" describe, say, SPI, but not what is sent over it. (Pages 19-23) - registers and the bits in them. The way this is presented varies a bit. Note than a mere register summary (pages 160-170) usually isn't enough. The usual form of presentation is a drawing of the register with the bits in them, followed a list or table of the registers and a brief description of what they do. (E.g., pages 30-32, 44-46, etc.) If the publicly available documentation contains all this material, then chances are that one can make a correct design incorporating the chip and also write the Free and Open software that uses the chip's functions. There can still be other obstacles, such as technical deficiencies or incompatibilities, lack of availability, high or hidden costs, etc., but one has at least the basics needed to continue with further evaluation. Thanks, - Werner _______________________________________________ Qi Hardware Discussion List Mail to list (members only): [email protected] Subscribe or Unsubscribe: http://lists.en.qi-hardware.com/mailman/listinfo/discussion
