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Common FAQs on Serial RS232 & RS422/485 Communications
Question: How far will RS232 communicate?
Answer: RS232 will reliably communicate up to 15 metres (~50 feet). It may be the case that with a well shielded cable in a noiseless environment greater distances can be achieved.
Question: How far will RS422/485 communicate
Answer: RS422/485 can reliably communicate up to 1.2 kilometres (~4000 feet).
Question: What is Autogating?
Answer: When the gating of transmitter and receiver lines are controlled through software (using RTS) in a multitasking operating system, it can sometimes take too long for a transmitter to become a receiver because the transmitter can not set RTS false quick enough. This means that when the transmitter finishes transmitting data it can potentially lose part of the response because it is unable to become a receiver in time. To overcome this problem Brainboxes RS422/485 devices have a hardware feature called autogating. This feature automatically detects that transmission is about to commence and gates the twisted pair to transmit. When the last stop bit has been transmitted the line is automatically gated to receive. This process happens very quickly at the hardware level (requires no software) and ensures that the transmitter is ready to receive a response as soon as it has finished transmitting. In detail, the driver will write bytes of data into the transmit holding register (THR) on the UART. When the driver has finished, the UART will remain in the same state for 1.5 bits then the transmit holding register empty (THRE) bit will be set, this triggers the card to gate the ouputs TX+ and TX- to become RX+ and RX-.
Question: What is a FIFO?
Answer: A FIFO (First In First Out) is a type of buffer, where the first byte to arrive is the first to leave. Brainboxes Serial Devices all have Hardware FIFOs. FIFOs reduce the chances of data loss by 'buffering' the data. This way the device driver can then read all of the data from the FIFO in one go, whilst communication is still continuing. If you imagine someone asking you to load apples on to a lorry. If they hand you one at a time they are likely to be ready with the next apple before you have got back from the lorry. If you ask them to fill a box however, whilst you take a box they can be filling the next box. This is how a FIFO works. You use what is called a trigger level to determine at what point (how full) the buffer should be emptied by the driver; or in the analogy how full do you let the box get before taking it to the lorry. Some Brainboxes cards have the standard 16 byte FIFO on it, but some have a 64 byte FIFO and Photon cards have a 128 byte FIFO. In an application where it may not be possible to implement flow control a very large buffer with a modest receive trigger level can significantly reduce data loss.
Question: What is Optical Isolation?
Answer: Some Brainboxes Serial devices are appended with the words Opto - Isolated. It may be the case that cards used in certain environments are susceptible to large surges of electricity which may potentially damage the card or the PC. Opto Isolated cards are isolated so that sudden surges in (on the wire) electricity (eg. lightning) do not damage the PC in which the cards are housed.
Question: What is the purpose of the buffer on a UART?
Answer: In the early days of serial communications buffered UARTS were not really necessary. This is because all operating systems were not multi-tasking ie in DOS for example you did not edit text and communicate simultaneously. With the advent of Windows and other multitasking operating systems it became necessary to both edit (using a word processor) and communicate simultaneously. This meant that incomimg data could be missed if a document was being edited. A buffer is an area of memory in the UART in which to store incoming data. It allows data to be stored physically in the UART which can later be serviced by a software driver.
Question: What is the difference between RS422 communication and RS485 communication?
Answer: RS422 is an earlier standard than RS485. If a card complies with the RS485 standard then it will comply with the RS422 standard. The most significant difference is that RS422 when using 2 wires to communicate to another device is simplex only, ie it can only transmit or receive in one direction and requires handshake lines to control the flow of data. RS485 is a standard which allows bi-directional communication when using 2 wires. This is accomplished on the Brainboxes card using a hardware feature called 'autogating'. The transmitter and receiver are gated alternately on and off to transmit and receive data.
Question: What is RTS / CTS Hardware Flow Control?
Answer: RTS / CTS Flow Control is another flow control mechanism that is part of the RS232 standard. It makes use of two further pins on the RS232 connector, RTS (Request to Send) and CTS (Clear to Send). These two lines allow the receiver and the transmitter to alert each other to their state. A transmitter raises its RTS line, which causes an interrupt on the receiver, i.e - hey can I send some data?. If the receiver is in a position to receive the data it will assert its CTS line, i.e - yes you can start sending. The raising and lowering of these lines allows device drivers which implement hardware flow control code to maintain a reliable data connection between transmitter and receiver. The advantage to this approach is that damaging data in transit does not effect the flow control mechanism (as in XOn / XOff).
Question: What is XOn / XOff Software Flow Control?
Answer: XOn / XOff is a software flow control mechanism. It can only be used in character oriented data transmissions (not binary transfer) as it relies on the use of a pre-determined XOn character and a pre-determined XOff character. The basic idea is simple, when the receiver buffer fills to the point it cannot receive anymore data it issues an XOff (Transmit Off) to the transmitter. When the transmitter sees the XOff character is stops transmitting. It will only resume once it sees a corresponding XOn. The disadvantage of such a system is that should an issued character become damaged in transit no action will be taken by the transmitter.
Question: Do you have support for 64-bit Windows operating systems?
Answer: If you have a 64-bit PC with a 64-bit operating system, the devices you have installed on the system will need to use 64-bit drivers. It will not be possible to use 32-bit drivers unless the operating system is 32-bit, which will still run on 64-bit PC�s.
Brainboxes has developed 64-bit drivers for their serial and parallel card using the beta versions of Microsoft�s 64-bit XP and Server 2003. These drivers have been thoroughly tested with a selection of serial cards in both XP and Server 2003 and are now available as a beta download. The tests were conducted in an Intel Pentium 4 EM64T system and an AMD Athlon 64 Pro 3000+ system. Further testing when Microsoft release the full version of 64-bit Windows operating systems will enable Brainboxes to create a full release. Ultimately these drivers will be available in one package which will include the 32-bit and 64-bit drivers.
Download the beta 64-bit drivers
We would appreciate any feedback you have to give on your experience of using these drivers.
Please email sales@serial-cards.co.uk
Information on 64-bit Windows and PC�s
64-bit Windows supports far more physical memory than current 32-bit operating systems � up to 16 terabytes, a huge step from the 4GB supported by current 32-bit systems. This jump will mean more applications can run simultaneously, and more of the data can be stored in the system�s main memory. Graphics, modelling and database programs, as well as games programs will all benefit from this increased processing power. 64-bit systems are also predicted to make progress in realising a real-time language translation systems and real-time video rendering impossible with 32-bit systems.
A 64-bit version of Windows is therefore likely to open up new areas of application as well as supporting higher-performance on each application, and allowing more users to work simultaneously on a single application. PC and server manufacturers are already building machines using processors from Intel (Itanium) and AMD (Athlon 64) capable of supporting 64-bit processing, so it is vital that all hardware components are available with drivers to support the higher-processing throughput.
Question: I do not have a Card Properties page in Device Manager??
Answer: Device Manager is accessed by opening the Control Panel, System, Hardware and then the Device Manager button. Depending on your operating system version and what product you have, there will typically be an entry for your serial card under Multifunction Adapters or Multi-port Serial Adapters.
Any settings that are selectable for the card i.e. Duplex Mode, can be changed by double clicking on the card's entry and then selecting the Card Properties tab.
If your Card properties tab is not there please try the following, which is applicable to 2000/XP only:
1. Go to Start and press Run. Type regedt32 to open the registry editor2. Go to the following folder HKEY_LOCAL_MACHINE\SYSTEM\CURRENT CONTROLSET\ENUM\PCI (or PCMCIA if applicable)
3. For PCI cards look for an entry with "VEN_135A" and right click it
4. Select 'Permissions'
5. Check the Full Control box to allow permission
6. Close the registry editor
7. Reboot the machine
8. Open Device Manager and the Card Properties tab is now be visible
Question: My UC-146, UC-607 or UC RS422/485 card is not working properly
Answer: The cards mentioned above require later drivers to the standard released software version 5.4.1, as they were developed after the standard software was released. The drivers can be downloaded from the following location: Serial Solutions and are labelled as being specifically designed for these cards.
If you still have problems using these drivers in 2000, XP or Server 2003 it may be because the operating system is searching the Windows Update site for a better driver during the installation. The standard release of the drivers is Digitally Signed and available for download by Windows Update and although the cards above require later drivers, because the later drivers are not yet digitally signed (though they pass all our internal Logo Approval testing), the operating system prefers to install the Signed Drivers.
To avoid this problem you can:
1. Right click on My Computer and choose Properties.
2. Select the Hardware tab and press the Windows Update button.
3. Change the radio option so that it selects Never Search Windows Update for drivers
4. Alternately, remove the network/modem cable from the PC during the driver installation.
When the next version of drivers is released they will be Digitally Signed and so this problem will no longer occur.
Question: I cannot get a UC card to work but my CC card is fine
Answer: The new range of serial cards available from Brainboxes have the prefix UC, which stands for Universal Card. These cards are able to work in both a 5v and 3.3v PCI slot and are backward compatible with the CC range of PCI cards that Brainboxes have manufactured for many years.
In order to support the new cards, the Serial Solutions drivers have been updated for Windows 98, NT, 2000, XP and Server 2003 families, therefore if you are using older drivers, you will need to uninstall and reinstall the latest drivers. These are available from the following web page: Serial Solutions. The uninstall program is located in the root of the folder and is called SSUnist.exe.
How do I set my RS422/485 device into half duplex mode?
Full duplex mode uses 4 wires to transmit and receive data. Half duplex mode uses 2 wires to transmit and receive data and can only transmit or receive at any one time. To set an RS422/485 device into half duplex mode both the hardware and the drivers must be set correctly.
Hardware
To set half duplex for a PCI or ISA card, connect the supplied jumpers across the header pins on the PCB so that TX+RX+ are shorted together and TX-RX- are shorted together. For a PCMCIA card, there are no headers on the card itself so the short must be created within the cable being used to connect the PCMCIA card to the other device. This is performed by shorting pins 1&6 and 2&7 using two pieces of wire.
Drivers
To set half duplex for PCI, ISA or PCMCIA card, for Windows 98, 2000, XP onwards access Device Manager and double click on the card�s entry to access the Property pages. For Windows NT go to the Serial Solutions Control Panel applet. Choose to change the card�s mode to Half Duplex mode.
Question: How do I install my PCMCIA card?
Answer: The Brainboxes PCMCIA cards are supported in Windows 98, 2000 & XP, with limited support in NT. The cards are not supported in DOS.
Please follow these steps:
1. Uninstall the current drivers by using the Uninstall Program
2. Download the latest Serial Solutions drivers from the website.
3. Reboot the machine and insert the card.
4. Follow the relevant instructions in the installation guide to install your card.
To install a PCMCIA card in NT:
The PCMCIA serial cards use Microsoft's own serial driver, and will only install as COM1 or COM2 - one of these will need to be free to install the card.
1. Insert the card into a free PCMCIA slot
2. To check that the card has installed, click on 'PC Card' in Control Panel.
3. Clicking on 'Properties' displays the COM port number.
Note: 2 port PCMCIA cards not supported in Windows NT and PM-120 is Full-Duplex mode onlyI am trying to install my PCI / PCMCIA card in Windows 2000 / XP and an error has occurred. Windows is asking for a .vxd file e.g. ssenum.vxd, or is looking for a Windows 95/98 file
It would appear that Windows has started to install the Windows 9x drivers from the CD instead of the Windows 2K/XP drivers.
Please follow these steps:
1. Uninstall the current drivers by using the Uninstall Program
2. Download the latest Serial Solutions drivers from the website.
3. Reboot the machine
4. When the Found New Hardware wizard appears following the reboot, choose to Install from a Specific Location and then browse to the folder where you have unzipped the downloaded drivers.5. The card will now install properly
Question: I have tried to install my PCI / PCMCIA card in Windows XP and it has installed incorrectly and displays an error code 41 when examining the Port�s properties from Device Manager
Answer: Most new laptops and desktops do not have on-board serial ports and so it appears that the standard Microsoft serial drivers do not automatically load.
Our latest Serial Solutions software has incorporated a fix for this problem.
Please follow these steps:
1. Uninstall the current drivers by using the Uninstall Program
2. Download the latest Serial Solutions drivers from the website.
3. Reboot the machine
4. When the Found New Hardware wizard appears following the reboot, choose to Install from a Specific Location and then browse to the folder where you have unzipped the downloaded drivers.
5. The card will now install properly.
If you still have problems installing the card properly following these steps please email support@brainboxes.com with details of your PC make and model, operating system and of the error code (if it is not code 41).
Question: How can I change the COM label(s) assigned to my card?
Answer: Earlier versions of the Brainboxes Serial Solutions software may have had problems with COM label changes. This has now been resolved however.
Please follow these steps:
1. Uninstall the current drivers by using the Uninstall Program
2. Download the latest Serial Solutions drivers from the website.
3. Reboot the machine and insert the card.
4. Follow the relevant instructions in the Changing COM labels guide.
Question: How do I test my PCI, ISA or PCMCIA card to make sure it is working?
Answer: Please see the Using HyperTerminal document
Question: What is the pin-out of the 'D' connector on my Brain Boxes Serial card?
Answer: Please see the Brainboxes Standards document
Question: What is the pin-out of the small connector on my PCMCIA card?
Answer: If you require the pin-out of the 9-pin D-type connector on the end of your PCMCIA cable, please see the following Brainboxes Standards document.
If you have a broken PCMCIA to 9-pin D-type connector cable, please contact sales@serial-cards.co.uk for information on how to purchase a new one.
If you need to create your own cable for a custom application, the following pin-outs on the PCMCIA connector apply:
RS422/485 Cards
1 - GDN
2 - TXD-
3 - RXD-
4 - TXD+
5 - RXD+
6 - RTS-
7 - CTS-
8 - RTS+
9 - CTS+
RS232 Cards
1 � GND
2 � DCD
3 � DSR
4 � RXD
5 � RTS
6 � TXD
7 � CTS
8 � DTR
9 � RI
Question: What is the cause of buffer overrun when transmitting data to my serial card?
Answer: There are two different types of buffer overrun: hardware and software buffer overrun. Both types of buffer overrun are more likely to happen when transferring continuous streams of large amounts of data across the serial port using high baud rates e.g. >1M baud.
The following white paper has been written to help explain the reasons for buffer overrun and the steps that can be taken to reduce it:
Buffer Overrun White Paper
I have tried to install my PCI / PCMCIA card in my PC and it has installed incorrectly and displays an error code 10 when examining the Port�s properties from Device ManagerA code 10 error message is typically a resource conflict problem, even though it may not be displayed as such in Device Manager.
Please follow these steps:
1. Uninstall the current drivers by using the Uninstall Program
2. Download the latest Serial Solutions drivers from the website.
3. Reboot the machine and insert the card
4. When the Found New Hardware wizard appears following the reboot, choose to Install from a Specific Location and then browse to the folder where you have unzipped the downloaded drivers.
5. The card will now install properly.
If the problems persists then please do the following:
6. Double click on the card under Multi Port Serial Adapters in Device Manager (Control Panel > System > Hardware) and go to the Resources tab.
7. Uncheck the 'Use Automatic Settings' box and select a different configuration setting from the drop down box; Configuration Setting 0007 for instance.
8. Then click OK, and close Device Manager.
9. Reboot the machine and reopen Device Manager to check that the card is now installed correctly.
If you still have problems installing the card properly following these steps please email support@brainboxes.com
Question: I am trying to install my 2-port PCMCIA card in Windows XP but it will not install properly.
Answer: Earlier versions of the Brainboxes Serial Solutions software did not support 2-port PCMCIA cards in Windows XP. This has now been resolved however.
Please install Windows XP Service Pack 1 on your PC before trying to install the card. The Service pack can be downloaded from the Microsoft website.
Please follow these steps:
1. Uninstall the current drivers by using the Uninstall Program
2. Download the latest Serial Solutions drivers from the website.
3. Reboot the machine
4. Follow the relevant instructions in the installation guide to install your card.
For further details regarding the need for Service Pack 1, please see the following Microsoft Knowledge Base Article detailing the problems with the driver �pcmcia.sys� in Windows XP, which is solved by the use of Service Pack 1.
(c)Brainboxes Limited 2003 - Acknowledgements to Brainboxes of Liverpool, who compiled these FAQs on Brainboxes Bluetooth Products. Applicable to Brainboxes Bluetooth Products.
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