Legacy Serial Communications Protocols 

Modern networking standardisation

For decades, various communication protocols have been utilised to connect telecommunications and computer hardware devices over short and long distances. To avoid incompatibility problems, standards were formulated and agreed, but meanwhile, a continuous drive to provide improved performance has meant an evolution of various alternatives.

Today with the dominance of USB, there are connector types and associated data protocols that have become almost universal for the wired serial connection of new devices over short-distances (when the use of wireless alternatives like WiFi and Bluetooth are not possible or appropriate). Whilst Ethernet has become the preference for local IT networks, for long-distance telecommunications, fibre-optic transmission is providing the benefits of reliable high bandwidth services. 

Maintenance of legacy standards for connecting and communicating 

Despite this, many older infrastructure systems and devices continue to utilise historic protocols and connections, and so it is still of benefit to recognise and be able to maintain ways to interoperate. There follows a non-exhaustive overview and comparison of the most popular standards and types of serial data communication methods.

RS-232 (V.24 / V.28)

Introduced way back in 1960 by the Electronic Industries Alliance (EIA), this is probably the longest surviving communications standard, but over time due to various revisions and lack of uniformity of connector types and connections, incompatibilities can arise. This resulted in the need for conversion cables, gender changers, etc.

It is a serial, full-duplex, unbalanced, single ended communications standard which has limitations in terms of transmission distance, noise immunity and operating speed, and can only be used for point-to-point connections.      

Given its age, it pre-dates most of modern computing, and was established for the relatively new purpose of communicating between a teleprinter, designated as the Data Terminal Equipment (DTE) and a modem, the Data Communication Equipment (DCE). The standard defines a range of ‘circuits’ (pin assignments) which include data – TxD (transmit) and RxD (receive) – along with various control signals such as DTR (data terminal ready), RTS (request to send) and CTS (clear to send).

When directly connecting two DTEs, such as two computers without using modems, a ‘null modem’  or cross-over cable is needed to swap the connections between the transmit / receive data and control lines.

Over the years, this extended to the uses of connecting computers to various peripheral devices like printers, as well as to other computers. Most PCs then came to be equipped with a “D-Type” port, initially for 25-pin connectors but eventually 9-pin became much more common.

Voltage levels are defined for the signals, in the range of -3V to -15V i.e. negative voltage representing a logic ‘1’ (mark) and between +3V to +15V i.e. positive voltage as logic ‘0’ (space). The range between -3V and +3V as invalid, and typically voltages are expected between +/5V to +/-12V whilst peak voltages can up to +/- 25V.

RS-232 TTL

This variant to the RS-232 standard is designed for more convenient interoperation with low voltage circuits over shorter transmission ranges. This specifies a positive voltage of +5V representing logic ‘1’, and 0V for logic ‘0’, which unfortunately can cause operational difficulties through confusion regarding the deployed types. Naturally, this requires correct interfacing and use of converters to provide the required voltage level shifting and inversion between variants.

RS-423 (V.10 / X.26)

Originally designed and launched in 1975 as a replacement for RS-232, offering longer distance and faster speed communication, it failed to become widely adopted. It did however feature on the BBC Micro in the 1980s, utilising an unusual 5-pin DIN connector.

Sharing similarities with RS-232 as a serial, full-duplex, unbalanced, single ended communications standard, it notably adds multi-drop capability, making it possible for one transmitter to send data to up to 10 receivers.  It’s voltage range is restricted to +/- 6V, with the driver output between +3.6V to +6V representing logic ‘0’ and -3.6V to -6V for a logic ‘1’.

RS-422 (V.11 / X.21)

This standard, also launched in 1975, provides serial, simplex, balanced, differential communications. Like RS-423 it provides multi-drop capability for one transmitter and 10 receivers.

It was more successful as an upgrade to RS-232 as it provided better noise immunity through the use of twisted pairs of conductors carrying two differential data lines. Full-duplex communication is provided by using 4 wires and two transmitters and two receivers to send the data in both directions.

The differential voltage between the pair of transmit lines and pair of receive lines determine the logic states, rather than the nominal 0V to 5V signals compared to ground, with the maximum common-mode voltage in the range +/-7V.

Typically, line A (or Y) is labeled TxD- / RxD- and is the non-inverted signal and line B (or Z) is TxD+ / RxD+, which is the inverted or complement of the same signal. Then B greater than A usually represents logic ‘1’, following the RS232 convention that this state is represented by a negative voltage, in this case line A of at least less than -0.2V with respect to B. Conversely, A higher than B by at least more than +0.2V, therefore represents logic ‘0’.

It is important to assign these lines correctly; for instance, on a Nokia DM2 multiplexer, the UR / UT specifications for the MI service interface assign logic ‘1’ to a negative voltage, but this doesn’t make it clear whether this is referring to B >A or A > B. In practice, this can be addressed simply by reversing the two input and/or the two output A & B connections should the opposite assignment apply.       

RS-485

This standard came out in 1983, and brings further enhancements over RS-232 whilst retaining a degree of backwards compatibility with RS-422. It provides serial, semi-duplex, balanced, differential communications. Like RS-422 it uses twisted pairs of differential data lines to provide improvements to transmission distance, noise immunity and operating speed. But through use of bidirectional transceivers, it only requires 2 wires to provide both directions of data transfer (though not at the same time, i.e. semi-duplex).

This can be upgraded to 4 wire full-duplex operation by adding an additional pair of transceivers, but in practice this is not necessary unless for interworking with existing RS-422 components. It extends transmission capability to true multi-point communication, with the possibility for use of up to 32 transmitters and 32 receivers, by means of a tristate mode so that drivers are switched off when not transmitting.    

Usually, line A is named D- as the non-inverting signal and line B is its complement, the inverted signal named D+, such that when the voltage of D+ is high, D- is low. With B greater than A by +0.2V then this represents logic ‘1’. The opposite polarity, resulting in a voltage difference of B lower than A by -0.2V, is therefore logic ‘0’.

Its improved maximum common-mode voltage range of -7V to +12V aids its ability to operate in multi-point configurations, allowing for wider differences in ground potential between the drivers and receivers.              

Conversion between RS-422 and RS-232

This naturally loses the RS422 advantages of differential data for noise suppression and transmission distance.

For RS232 a negative voltage is logic ‘1’; when the device transmits this to the RS422 RxD- or A input the differential voltage with respect the RxD+ or B input held at GND is B > A i.e. logic ‘1’. Whereas with a positive voltage from the RS232 device the RS422 input differential voltage is A > B, equating to logic ‘0’. 

However, when the RS422 TxD- or A output is low it could be the case that this not as negative a voltage as the -3V the RS232 device is expecting, and so technically is invalid according to the specification. However, in practice for many devices their operating threshold is beyond -1.5V and since B > A it is interpreted anyway as logic ‘1’. When the RS422 TxD- or A output is high, A > B which results in logic ‘0’ at the RS232 receiver.

Interconnection of  RS-485 and RS-422

Since RS-485 transceivers are generally ‘backwards compatible’, they can be applied to interface with existing RS422 devices. For full-duplex communication, 2 transceivers are used in the 4-wire configuration of RS422, and the semi-duplex capabilities of RS485 are ignored. Plus the RS422 restrictions of only one driver and up to 10 receivers per transmission direction apply. 

The RS422 driver TxD+ and TxD- lines are respectively connected to the D+ and D- pins of a RS-485 device acting as a receiver. Similarly, the D+ and D- pins of a RS485 device acting as transmitter are connected to the RxD+ and RxD- lines of the RS422 receiver(s). 

Comparison with USB

Whilst USB has become the De Facto standard for modern short distance wired connections, it is useful to compare this against the legacy protocols in order to understand the similarities and differences, and why it may be important to maintain or even extend existing interconnections.

USB 1.0 / 2.0 provide serial, semi-duplex, balanced, differential communications, analogous to RS-485 whilst offering much faster communication packaged in a smaller and more convenient 4-pin form-factor.

USB 3.0 uses two additional pairs of conductors in a compact 9-pin connector to operate full-duplex like RS-422, whilst maintaining backwards compatibility with older USB connections, and provides various further improvements including even faster ‘SuperSpeed’ transmission. 

However, USB only provides for point-to-point connections, with lower power and limited to TTL voltage levels, and as a result shorter transmission distances.

In conclusion, the choice of use depends on the various differing applications such as the interconnection of computer peripherals, industrial control, remote monitoring and multi-device connections. 

Consequently, for legacy interworking and improved performance over longer transmission distances with wider voltage ranges, dedicated USB to RS-232 / RS-423 / RS-422 / RS-485 converters are available.

Keeping Customers Operational

@YellowsBestLtd with our aim of Keeping Customers Operational assist with seeking out new products and legacy equipment spares to maintain new and well-established systems, as well as built-to-order cables and connectors to suit exact requirements.

We would be keen to hear your experiences of using communications protocols and whether we can be of any assistance with your solution requirements for legacy systems and new technologies, so please get in touch!

Challenging times demand time for a change!

New “UK” launch

It’s been a challenging time for businesses generally, and particularly in the United Kingdom, with Brexit in many cases adding cost and time to trading, and Covid-19 restricting travel and networking.

So it seemed an appropriate time to launch a new varient of the Yellows Best Limited website, now additionally utilising “.co.uk” as a signifier of commitment to our home market location.  

Keeping Customers Operational

The new YellowsBest.co.uk promotes the same blend of Services and Solutions for “Keeping Customers Operational”, but presented in a different and modern single-page layout, making it particularly mobile device-friendly where ‘vertical scrolling’ is more appealing than using the traditional ‘horizontal tabbed’ layout.

We hope this provides Customers old and new with a welcome alternative, though the original YellowsBest.com will continue to be maintained, along with it’s associated blog for ‘informal’ views and news updates.

Assisting with your requirements

It would be interesting to receive feedback as to how useful you may find this additional site, and whether there is anything else you’d like to see featured.

Of course, @YellowsBestLtd online content ultimately serves the purpose of highlighting the types of services and solutions we can provide. Customers may therefore be prompted to get in touch to discuss their specific requirements, which we can usually assist with.

Rest assured, if you use either contact address:

enquiries@yellowsbest.co.uk

enquiries@yellowsbest.com

we’ll receive your message and will be in touch by return. We look forward to hearing from you! 

Celebrating our fifth anniversary!

Five years of successful trading! Thanks to all our Customers and Suppliers.

@YellowsBestLtd has been in business for five years.

5 years of trading
5 years of trading

Our aim continues to be “Keeping Customers Operational”; understanding requirements and fulfilling them by providing a range of management services and solutions, including:

  • consultancy, for business development, sales and marketing
  • technical support, onsite engineering or 24/7 NOC remote assistance
  • systems supply, including legacy IT servers / workstations
  • spares for infrastructure, such as telecoms and CCTV cameras
  • repairs at module and component level, e.g. LED displayboards, PSUs
  • value recovery through reverse logistics, resale and recycling

As we continue to move forward, we’d very much like to understand what other services and solutions we can provide to our existing Customers, as well as what would be of interest to potential clients. We’re always keen to enhance our range of #business services, increase the #enterprise infrastructure we support and expand our mix of #sustainable solutions we offer for supply and maintenance of new and legacy #technologies and products.

Please get in touch to discuss your challenges; whether you’re implementing new systems or maintaining existing infrastructure to serve your operational business needs. We look forward to hearing from you.

Apple macOS 64-bit transition – Software ‘Legacy’ issues

32-bit Application compatibility Issues resulting from macOS updates

Issues have started to appear using existing and older software applications on Apple Macintosh computers with the transition from 32-bit to 64-bit operating systems, commencing with macOS High Sierra 10.13.4, and it’s set to get a whole lot worse!

Current Difficulties

Noticeable problems with applications have surfaced with the update to macOS Mojave.

Strange and unwanted things have crept in. For example:

  • opening a new Finder window causes a new tab to open instead. It’s like the wrong option has been selected – now opening a tab or a window are incorrectly identical. If you want a new Finder window, you need to then select ‘move this tab to a new window’. So suddenly this is a two-stage process 
New Finder window opens a New Tab instead
  • Trying to print from Microsoft Word causes the application to ‘crash’. The work-around for this is its still possible to print by using the toolbar button, instead of selecting ‘print’ from the drop-down menu. But then this doesn’t allow for changing print settings etc.
Microsoft Word quits when trying to print

Promise of worse compatibility problems

This is just the ‘tip of the iceberg’. A whole range of software applications which currently run happily on the Apple Mac are set to become unusable in the next update to macOS. We’re talking about mainstream applications such as Microsoft Office as well as ‘niche’ applications that you may utilise. This appears to represent the biggest shift in software compatibility since the change from Mac ‘Classic’ (OS 9 and before) to Mac OSX, more than 10 years ago.

A warning is displayed when a 32-bit application is launched in macOS High Sierra, and in macOS Mojave the alert appears every 30 days.

The official Apple advice is to ‘contact the application developer’. For the average user, that’s unlikely to achieve anything, particularly for mature applications that perhaps are no longer available or don’t have ongoing development. With something like Microsoft Word, then it should be possible to obtain the latest version, but naturally that will require a new purchase and/or an annual subscription.

Purchasing a new version of existing software will be an expensive business to just maintain your existing functionality

Maintenance Decisions

The standard maintenance advice for computers is to upgrade to the latest available version of operating software; that way, security patches are up-to-date, keeping the system secure, with new functionality as well as bug fixes provided, and support for the latest applications.

On this occasion however, it is worth taking a long considered look at the benefits of upgrading verses sticking with your current macOS release. If you haven’t yet moved to macOS High Sierra 10.13.4 or macOS Mojave 10.14 then you may wish to stay where you are for now, particularly if you’re happy with your current applications and functionality, such as Microsoft Word 2008. If you’re contemplating upgrading, either because you ‘must’ for security purposes or need to support a new generation application, then it will be worth taking the time now to review all of your existing software and work out what the upgrade path will be, or find out what the alternatives you could migrate to e.g. Apple’s ‘Pages’ to replace Microsoft Word, etc.

The most worrying situation will be for owners of specific hardware e.g. the M-Audio USB Midi interface, which may not (and never will) have a suitable updated driver software alternative

In such circumstances of uncertain application support, backups are as always essential; ideally you should be in a position to ‘roll-back’, dual-boot and/or run virtual machines to maintain previous applications and functionality. 

Consideration should also be given to maintaining a dedicated computer at the existing macOS version, and over time, migrating day-to-day applications (where they can be) to a new computer, keeping the old machine for ‘legacy support’.

Further Assistance

Take a look at the full Apple announcement about the transition to 64-bit technology and how it affects 32-bit apps.

@YellowsBestLtd satisfies new and ‘legacy’ requirements for the maintenance of systems and networks by providing services, such as technical assistance and hardware repairs, and solutions, including the supply of spare part items and software support.

We would be keen to hear from you regarding your operational needs, please get in touch.

Keymile UMUX – Multiservice access solutions

Comprehensive Functionality

The UMUX platform provides carrier-grade reliable multi-service multiplexing and aggregation functions over copper and fibre networks. A variety of voice (POTS, FSX, FSO, ISDN) and data (e.g. G.703, V.11, V,24, V,35) interfaces, SHDSL and Ethernet (including PoE+ and EoS) services are available. 

The modular and flexible housing provided by the UMUX 1500 (8U, 21-slot) and UMUX 1200 (4U, 8-slot) 19” subracks provide the perfect solution for all applications and locations, offering redundant controller and power supplies.

‘Legacy’ telecoms history

The UMUX SDH product portfolio was originally launched 1991 by Ascom, which subsequently became Keymile.

In 2003, by when 70,000 units had been deployed worldwide, the ‘enhanced’ UMUX multiservice access platform was introduced, offering the delivery of ATM, TDM and IP based services from the same platform, with support for IP/Ethernet, ADSL, VoDSL and G.SHDL.

Keymile was sold to ABB in 2017 when the UMUX range was discontinued, and then was acquired in 2019 by DZS. 

Continuing to provide operational service

The UMUX, together with the UNEM network management system and ‘sister’ LINERUNNER and MILEGATE products, continues to provide operational service with various global Operator, Utilities and Transport companies. 

@YellowsBestLtd supports requirements to maintain these networks by supplying various spare part items from refurbished and surplus stocks in perfect working order.  

There follows a list of the main elements that are typically provided, though other items can be provided. Please let us know of any specific requirements you may have. We look forward to being of assistance.

Part CodeUnit typeDescription
A31A1679U1500-CSU1500 Core R2 (DC) for 19″ mounting (incl. Subrack, POSUM, COBUX 128x2Mb/s XC)
A30A0205DATAS-FUData Interface unit.  Multi-Interface V.35, V.24/V.28, X.24/V.11, RS485, Ethernet, 4 ports, all options
A24A3323LOMIF-FU2 Mb/s IF (E1), 8 x G.703 Interfaces
A24A3651COBUX-FUControl Unit Standard,128x2Mb/s XC
A21A2865EXLAN342POTS FxO Interface Unit, 12 ports, complex impedance
A31A7871GECOD371Data IF 64kb/s G.703 codir., 8 interfaces
A24A3338LOMI4-FU2 Mb/s IF (E1), 4 x G.703 Interfaces
A24A7979POSUM306Power supply unit -48VDC 85W
A30A1442SUBH3-FUPOTS FxS  Interface Unit, 30 ports
A31A7873SULIS393ISDN Interface Unit Subscriber side, ISDN BA 2B1Q, 8 interfaces
A23A9927SYNAC-FUSDH Access bridging unit SBUS-PBUS, 8xVC-12; no external IF
A24A1989TUPON-FUOptical Trunk Interface 8Mbit/s 1xopt.(o), 4xel.(e), 1550nm, PBUS access


PC Troubleshooting Project

Stop Code: PROCESS1 INITIALIZATION FAILED

As a result of a PC replacement and upgrade project for Action for Asperger’s, we were presented with a seemingly serviceable Dell Optiplex 755 machine but suffering from a critical failure on power-up, meaning that the computer was unable to boot into windows, preventing use and severely limiting the diagnostics and configuration options.

PC restart

The first step following a reboot was an automatic ‘startup repair’, however, this didn’t result in a fix:

Startup Repair

Rebooting again and selecting F2 during the initial boot-up screen:

Boot Up

enabled a look at the system information, which indicated that the PC hardware was fine.

System info
Processor info
Memory info

As an extra measure, the internals of the computer were briefly examined, ‘reseating’ components including the video board, memory chips and hard disk and then the system test run to verify all was well.

Internal
Test

It was concluded therefore that the PC hardware was not the cause of the difficulties, and that the Windows installation was severely compromised. 

From the bootup, troubleshooting was selected

Choose an option

From the ‘advanced options’, the Command Prompt was accessed.

Advanced options

Using these commands:

DISKPART

SEL DISK 0

LIST VOL

It was possible to view and confirm the drives and their assigned letters.

Diskpart

Extra information was provided using this command:

wmic logicaldisk list brief

Progress was further hampered by the internal DVD/CD drive not being recognised on boot-up, in its place an external DVD drive was connected.

Rebooting and pressing F12 on power up enabled the adjustment of the Boot priority, selecting the DVD drive first.

A copy of the Boot Repair Tool by yannubuntu was next downloaded and a boot-repair-disk created

This was run from boot and gave encouraging results:

Boot Repair Disk

Alas, these steps hadn’t cured the problems, now a further critical error message was displayed:

Recovery

Consequently, using the Microsoft USB/DVD Download Tool, a Windows 10 install disk was created (confusingly the site specifies Windows 7, but it works fine for Windows 10)

This was booted and the appropriate selections made for a fresh installation of Windows 10:

Windows Setup
Windows Install now
Windows type of installation
Windows operating system selection
Activate Windows
Applicable notices and licence terms
Partition choice

At this point, it was found necessary to delete the old windows partition, extend a different partition and create a new partition in order to be able to commence the windows installation.

Partition selection

It did however then allow the installation of Windows onto the other partition, meaning that two bootable volumes were created. Might be useful for future upgrades or troubleshooting.

Choose OS

Just the straightforward matter left of completing the user configuration of the operating system ready for use. 

Choose region

All done, pleasing to conclude that the critical issues with this PC could be resolved through software corrections alone! 

@YellowsBestLtd provides professional Management Services for Business Development activities and Enterprise Support of Infrastructure. We source Solutions for Sustainable Systems maintenance, equipment Technologies and telecoms and other Products to enhance operations.

We’re always keen provide whatever is needed, so please let us know anything you require.

Nokia ‘Dynanet’ Telecoms – Stock disposal

‘Last chance’ for spares!

The Nokia ‘Dynanet’ family of PDH Transmission telecoms products has served customers well for the last 20+ years, and indeed some networks continue providing good operational service. 

DM2
Dynanet Subtrack

@YellowsBestLtd has supported requirements to maintain these networks by supplying various spare part items from refurbished and surplus stocks in perfectly working order.

However, demand has recently reduced and warehouse space is needed, so now the time has come to recycle / dispose of a large proportion of the remaining equipment. Consequently, there remains a short-term opportunity to obtain any items still required to maintain existing deployed infrastructure, before the products are gone.

Here is a stock list of the main items currently available, though there may be a few additional parts that can be supplied. Hence, please check and if you do have any requirements, please let us know – before it’s too late! We look forward to hearing from you.

Part  NumberDescription
24204TPSO H/W Module
CC 24002DB2 Branching Unit, B2 2×2 Mb/s 75 ohm
CC 24011DB2 2 Mb/s Switching Unit, X2 75 ohm
CC 24101DN2 Interface Unit (IU2) 2×2 Mb/s 75 ohm
CC 24111DN2 Control Unit (CU) 75 ohm
CF 24186DN2 19″ Subrack
CF 24186.09DN2 Subrack 19″, grey-L91 EMC
CG 24170DN2 Bus Power Unit (BPU)
CG 24171Extended DN2 Bus Power Unit (EBPU)
CU 24013Data Interface Unit (DIU) 2M, nx64k: G.703/704, 75 ohm
T30506.0917-slot DYNANET Subrack
T30851.02Subrack Power Adapter (SPA)
T37870.01NDM ACM2 19in 17-slot subrack
T37871.01NDM DN2 19″ 17-Slot Subrack
T37882.01NDM DC Unit (NDUe)
T37882.02NDM DC Unit (NDUe)
T37885.01NDM Ring Generator
T37889.01NDM Backup Unit (NBU)
T65520.01ACL2 RM DC Power Gen
T65580.01ACL2i PF GEN Line Terminal Card
TA 21513Optical Line Terminal Repeater 2-8 M, 1300 nm LED MM/SM
TA 21516Optical Line Terminal Repeater 2-8 M, 1300 nm LASER SM
TC 21101DM34 Mux Card
TC 21301DM8 Multiplex Equipment, 75 ohm
TC 21705Supervisory Substation
TC 21710.01TMS Adapter
TG 21261Ring Generator 25HZ 15W
TU 21122.5Data Interface Unit (DIU) 48..64k V.11 10ch
TU 21124Data Interface Unit (DIU) NX64k V.11/V.35/X.21 2CH
TU 21124.05Data Interface Unit (DIU)
TU 21125Data Interface Unit (DIU) 48..64k with sync, X.21
TU 21205Channel Unit SUB/SUB
TU 21206Channel Unit SUB/SUB
TU 21215Channel Unit SUB/EXCH
TU 21216Channel Unit SUB/EXCH
TU 21234.20Channel Unit E&M/VF-P, 10 CH, 20 E&M CH
TU 21236.10Channel Unit (CU) 8ch E&M/uP: 2xe&m/vf
TU 21255.01Channel Switch, 4 PORT
TV 21640.08Power Interface Adapter DC