I have to develop a driver for Realtek's rtl8188cus (WiFi USB dongle), but couldn't find any datasheet or any kind of how-to…
I contacted RealTek but they don't seem to respond.
Any advice ?
Electronic – Need Realtek’s rtl8188cus (WiFi USB dongle) datasheet. Any advice
datasheetusb devicewifi
Related Solutions
Via USB? It would be difficult as you've been replied to. But, if the underlying device communicated on a hobby-friendly bus such as SPI or I²C, it would make things a lot more possible. Obviously, this would require in-depth knowledge of the hardware which would be impossible to come by and difficult to derive. In short: no; this is simply not worth the time and effort required and may not even be possible anyways.
Postscript:
A closer look at the WiFi module circuit diagram indicates that what I have written below MAY be incorrect. Rather than delete it for now until I can look into it further I'll leave it for David to look at as it MAY be useful.
Others may ignore it :-).
I'll try and get back to it later and David may have commented by then.
Work calls ... ;-)
Note that WiFi RXDIN connects to SENS0 on pin 34 and also to URX on pin 12.
This may allow some form of level detect and shift.
References at end should be useful.
Based on available data sheets and manual, you appear to have an RS232 level incompatibility issue. The WiFi module is using +/- 10 data signals. The USB-UART dongle is using 3V3 or 5V data signals.
There is probably an inverted polarity issue as well.
Given the voltage levels used in each case:The WiFi module probably uses inverted logic levels
where negative output / DC low / V- = logic 1 = logical high,
The USB-UART dongle probably uses standard logic levels
where positive out / V+ = logic 1 = logical high.
If this is what is happening it would explain what you are seeing.
The WiFi unit sees inverted (to it) polarity signals at a level which may or may mot always trigger it's input gates. When it does respond it outputs signals which are inverted in polarity to what the dongle expects and at excessive voltage levels.
The above is easily enough checked by measuring the voltage on TX out at the connectors in each case with the devices not connected to each other.
WiFi module TX out idle
Data sources listed at end.
The diagram below is for the "Roving Networks RN131G WiFi module".
Assuming that it is the same as your RN131 -
External data in line = RXDINJ (as shown on diagram below)
Data in at IC U2 = RXDU2 (called SENS0 on diagram)
The IC U2 operates from 3V3.
The RXDIN line at right middle has a 22k/10k R60/R61 voltage divider.
This gives a 3.2:1 division of the data signal.
If data high is expected to be no more than 3v3 at RXDU2 on IC U2 then this allows an up to
3.2 x 3v3 = 10.6V data signal on RXDIN.
If the IC accepts Data_in_high of as low as say 70% of Vdd then minimum data in at the IC U2 = 3v3 x 70% =~ 2.3V.
To achieve 2.3V minimum at the IC would require a RXDIN data in signal of
3.2 x 2.3V = 7.4V.
As the USB-UART interface dongle expects a 3v3 "TTL" interface (or 5V depending which datasheet line you read) it will not each a valid
c:\zzz\RN131G WiFi module
They say
... The RoHS compliant PCB assembly is configured with a fixed TTL output level of +3.3V.
Deriving its power from the USB bus connection, ...
RN-SRL-PRO3V-DGL: USB to 3V serial UART dongle, Prolific chipset, USB connector, bare PCB 5V serial
connection
More soon ...
Related Topic
- Electronic – Adding WiFi to OSLess embedded device
- Where to start building this wifi video streaming circuit
- Is it possible to use a USB Wifi dongle with STM32F429I Discovery board
- Electronic – Avastar SP88W8782 wifi module Pinout 12 pin usb
- Electronic – How to plug the homemade Yagi Antenna into a wifi USB dongle
Best Answer
I expected this to be a problem of an OEM-only part with everything under NDA and binary drivers provided. You'd need to be planning a large-volume order (and have the company letterhead to prove it) to get anything that could help you write a driver for many components like this.
So no, don't expect this to be as simple as Googling the part number and finding the datasheet in the top link.
I went to the Realtek site and looked for documentation, expecting to post a link to the "Volume orders only" page. However, I was pleasantly surprised when I went to the WLAN NIC > IEEE 802.11b/g/n Single-Chip > Software page and found Linux drivers. I had expected Windows binaries, but figured you're probably running an embedded Linux stack, and was about to post some information on configuring your real-time embedded Linux stack to accept the drivers designed for desktop Linux (Ubuntu 10.10, in this case). However, I waited for a moment and let the download finish. On opening the file "92ce_se_de_linux_mac80211_0005.1230.2011.tar.gz", I was still more pleasantly surprised to find C source code! And a readme! And release notes! And firmware binaries to flash to the chip! There are even comments in the code! And, the most surprising thing of all, there's even an email address to contact the maintainer, Larry Finger, who is also listed on linuxwireless.org/en/developers/maintainers.
The datasheet is probably still under NDA, but you don't need to write drivers. You have them already written for you.
Do note that the source is under the GNU General Public License, Version 2. If you use this code in your project or make changes to it, you must release it and anything into which it is compiled (likely including the OS) to anyone who receives the source code. That includes customers who purchase your device and receive the source code as firmware flashed into it. That's a small price to pay when you consider that you have the driver source code available to you already.