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ChipWeb Wireless FAQ
Frequently Asked Questions for the Iosoft ChipWeb Wireless 802.11b development kit
We strongly recommend you set up a new 'scratch' wireless network for your experimentation, rather than using an existing one. The simplest network uses 'ad-hoc' mode, where you only need another PC with a PCMCIA (PC card), USB or PCI wireless network interface - the manufacturer is unimportant, so long as it is 802.11b-compliant.
'Infrastructure' networks are more common, and based around an 'Access Point', which is effectively a hub for wireless communications. Access Points also have an Ethernet connection, so you can use them to bridge between wired and wireless networks; some have advanced routing and firewall capabilities, but these can be a liability when first setting up a test network - start with the simplest device you can find.
The ER21 has one IP address, but two hardware (MAC) addresses, one for each interface. The PC maintains a record (ARP cache) of the last-known hardware address, and will continue to use it, even if you have switched network interfaces. The quick way to eliminate this ARP cache is to use the ARP command in a DOS box, giving the IP address of the ER21
ARP -d 192.168.0.20
This flushes out the old IP-to-MAC address mapping, and forces the PC to fetch the new MAC address.
The software is compatible with PCMCIA (PC) 802.11b cards using the Intersil PRISM2 , 2.5 and 3 chipset. The Netgear MA401 card is supplied with the ER21 and ER22 kits, and we do recommend this card.
Customers have reported success with D-Link DWL650 and Linksys WPC11 PCMCIA & WCF11 Compact Flash (CF) cards, though it is essential to check compatibility before using an alternative card. The ER21 hardware powers the PCMCIA card at 5 volts, so 3.3 volt cards can not be used.
Some cards such as the Linksys WPC11 version3, or the Senao/Engenius 2511 plus, claim to be dual-voltage but are always powered at 3.3V when used in laptops, and we have experienced difficulties getting them to work at 5V.
See question 16 for more information on 3.3V compatibility
No. Although the ER21 has both Ethernet and Wireless interfaces, and responds to Web accesses on both interfaces, the standard software does not include a router capability (i.e. it does not transfer network frames from one interface to the other). A skeletal router could be implemented, but the 1.5KB RAM in the PICmicro would place severe limits on its functionality.
Yes. The ER21 has a very similar hardware layout to the existing PICmicro networking board, so the ChipWeb Ethernet and serial drivers run without modification. The addition of the wireless interface has introduced significant extra complexity, but we have tried to minimise the changes needed to the top-level code when switching from a wired to wireless interface.
7. The new ChipWeb v2.17 code has new features (such as long EGI variable names) I'd like to use on the PICDEM.net - is the software still compatible?
Yes, you can treat ChipWeb v2.17 as an upgrade for the v2.02 release supplied in 'TCP/IP Lean' 2nd edition; the wireless extensions can easily be disabled, and the LCD support enabled, so that it runs on a PIC18xxx PICDEM.net board.
The current release is based on the PIC18F452. The PIC16xxx series can't be used as it has insufficient ROM.
The first release requires a recent version of the CCS PCH or PCWH compiler; it was tested with v3.110. The Hi-Tech PICC18 compiler v8.20 PL2 may also be used, see the application note www.iosoft.co.uk/docs/cw217notes.pdf.
Version 2.21 and later of the source code accommodates CCS and Hi-Tech compilers, including PICC18 v8.20 PL3 and PL4.
The average ER21 current consumption is around 250 mA, of which the PCMCIA card takes about 200 mA, assuming power management is disabled (see next question). The temperature of the voltage regulator can be reduced by dropping the supply voltage (minimum 7.8 volts), or adding a heatsink
In v2.21 or later software, there is a serial configuration option to enable the PCMCIA card's Power Management facility, which roughly halves the card consumption when in infrastructure mode. Unfortunately it does introduce a noticeable delay to all network transactions, which may be unacceptable in some high-speed applications.
The ER25 has a separate high-efficiency power supply for the wireless card which may be shut down by the microcontroller, a major power saving if communications are infrequent.
The two most common causes are the use of a Microchip In-Circuit Debug adaptor, and incorrect PICmicro configuration settings.
The Microchip in-circuit debug interfaces (ICD and ICD2) use port B pins 6 and 7 to communicate with the processor, and these lines are driven by the ICD even when debugging is disabled. The same lines are used on the ER21 as PCMCIA address lines A6 and A7, so the PCMCIA interface will fail if an ICD is connected. If an ICD has been used to program the PICmicro, it must be disconnected before the software is run.
PICmicro configuration settings:
Although not recommended in 'TCP/IP Lean' appendix D, it is advisable to enable the power-up timer, as it gives extra time for a slow LCD to settle after power-up.
There are a wide variety of setting methods and terminology used by device programmers, and the fuse settings in the hex file aren't necessarily propagated into the programmer, so it is wise to check the settings before programming a device.
If you are using P18WEB v2.17, be sure to read the software notes www.iosoft.co.uk/docs/cw217notes.pdf
The PCMCIA card uses almost all of the PICmicro I/O pins, so the ER21 does not include any specific provision for attaching other I/O devices (there is no I/O expansion connector). However, the following I/O lines might be useful
The easiest way to add extra I/O devices is via the 2-wire i2c bus, for example one or more Philips PCF8574 devices could be used, each device providing an extra eight bi-directional I/O lines. Alternatively, the RS232 port could be used to communicate with another microcontroller that performs the I/O functions.
The ER22 and ER25 cards are designed for easy I/O interfacing.
The ER21 is the original development board with a PICmicro, WLAN and Ethernet interfaces. The ER22 has the following changes
The ChipWeb software has been updated to accomodate the new boards, see ChipWeb version information for details
If you are new to the PICmicro, check out our beginner's guide
In addition to the ER21/ER22/ER25 hardware, you will need
If you have used an ICD to program the PICmicro device on the ER22/ER25, it can also be used for debugging, though for professional code development we do recommend using an in-circuit emulator such as the Microchip ICE2000.
No, the ER21 and ER22 power the card at 5 volts. You can't just drop the supply voltage, because the Ethernet controller requires a 5V supply. Also, 3.3V-only cards have special PCMCIA keying to prevent their insertion into 5V slots.
The ER25 is designed for use with 3.3V cards.
The most probable cause is the power, a regulated supply of at least 6.5V 500mA capacity must be used. Inadequate or unregulated supplies will cause erratic operation.
No, the limitations of the PICmicro RAM size prevent us from using a a standard socket interface. For details of the underlying program methodology see the 'TCP/IP Lean' book 2nd edition; it does not include any wireless networking, but does describe similar networking techniques using Ethernet.
© Iosoft Ltd. 2004 Version 6 28-April-04
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