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!

‘Legacy’ Infrastructure Ongoing Maintenance 

Continuing in Keeping Customers Operational

Over the last nine years, @YellowsBestLtd has sought out new, surplus and refurbished products and spare parts to assist with the aim of supporting Customers to maintain rather than replace their infrastructure networks, and as we enter our landmark tenth year, we continue to do so.

The alternative of wholesale replacements requires prohibitive investment costs and long project timescales to implement. And it can be the case that suggested replacements cannot provide equivalent operational lifetimes which therefore become obsolete faster than existing deployments.

Given the investment that has been made over many years, coupled with the fact may operational requirements have not changed, it makes sense to keep systems in place. By suppling spares, offering repair services and technical assistance, we are able to support these aims.  

Systems Replacement and ‘Value Recovery’

Eventually, it does become necessary or desirable to undertake network refreshes. Often, we can help evaluate, source and implement suitable systems.

As discussed recently at the Engineering Design Show, we are able to utilise the capabilities of a network of local manufacturers to replicate and if necessary reverse-engineer components and products to meet exacting performance requirements.  

When replacing existing networks, we are able to offer to Remove, Resell and/or Recycle existing equipment, generating revenue from the ‘Value Recovery’, and importantly ensure that items are disposed of in the most ethical and environmentally respectful way.

Equipment recently supplied and/or currently stocked

Certain product families continue to prove their excellent availability and reliability, and we are fortunate to continue to be able to provide stock of many of these items, either in new, surplus or refurbished condition.

Examples of  such products follow; should there be anything specific you require, please do not hesitate to get in touch; we look forward to hearing from you!

Nokia  ‘Dynanet’ PDH – Definitive Spares List

Keymile UMUX –  Multiservice Access Solutions

Marconi XMP1 –  telecommunications

Nokia, Marconi and Ericsson SDH –  Synfonet, SMA and OMS 

Sagem –  ADR SDH family

RadiFlow –  Cybersecurity Solutions for the Industrial IoT

TETRA –  Equipment and Terminals for PMR Networks

Bosch –  Professional CCTV Cameras

‘Dynanet’ PDH Telecom Spares

Continuing in Operation, Still Available for Supply

The ‘Dynanet’ product family is a range of PDH telecommunications products first launched by Nokia over 20 years ago. This equipment has proven to be incredibly reliable and dependable, extensively deployed by Operators, Utilities and Transport companies to provide resilient and highly available transmission networks.   

A continuing challenge for public and private network owners is the ongoing maintenance of infrastructure systems to support their business needs. In many cases, it makes sense to continue to operate legacy systems which are still fulfilling unchanged requirements, rather than contemplate costly and time-consuming change-outs and replacements. 

Keeping Customers Operational

@YellowsBestLtd seeks out new products and legacy equipment spares to assist with these aims. Recent enquiries have been fulfilled supplying refurbished and surplus stocks of equipment cards, as well as built-to-order cables and connectors to suit exact requirements.

There follows a few examples of items we have recently supplied. Also, our more extensive Definitive ‘Dynanet’ spares list here provides details of many items still available from surplus and refurbished stock. We would welcome any enquiries for the supply of similar or alternative parts, or support services to provide hardware repairs. Please get in touch; we look forward to hearing from you!

Example items, recently supplied

Multiplexers
Part NumberProduct CodeDescription
CC 24002DB2 B2DB2 2×2 Mb/s Branching Unit (B2), 75ohm
CC 24002 – DB2 B2

Multiplexers
Part NumberProduct CodeDescription
CC 24011DB2 X2DB2 2 Mb/s Switching Unit (X2), 75ohm
CC 24011 – DB2 X2

Multiplexers
Part NumberProduct CodeDescription
TC21101DM2DM2 Multiplexing Unit, 75 ohm

Mechanics
Part NumberProduct CodeDescription
T37870.01SUBRACKNDM 19in 17-slot Subrack
T37870.01 – Subrack

Power Supplies
Part NumberProduct CodeDescription
T37882.02NDUeNDM DC Unit (NDUe)
T37882.02 0 – NDUe

Voice Interfaces
Part NumberProduct CodeDescription
TU21236.10VF E&MCU 8ch E&M/uP: 1xUKe&m/VF
TU 21236.10 – VF E&M

Optical Line
Part NumberProduct CodeDescription
TA 21513DF 2-8Term. Repeater 2-8 M, 1300 nm LED MM/SM
TA 21513 – DF 2-8

Copper Line
Part NumberProduct CodeDescription
T65570.01ACL2iACL2i DC GEN
T65570.01 – ACL2i

Management
Part NumberProduct CodeDescription
T31094.01DCNDCN Adapter C4.0
T31094.01 – DCN

TETRA Equipment and Terminals for PMR Networks

Public Safety, Utility and Transport organisations over many years have deployed Private Mobile Radio (PMR) infrastructure equipment with high availability and reliability to provide to provide dedicated, secure communications networks.

Modern implementations of PMR utilise the digital TETRA standard, which provides interoperability between systems and terminals from a range of manufacturers.

@YellowsBestLtd our mission is  “Keeping Customers Operational, by continuing to provided spares solutions, hardware repairs and support services to ensure continued long-term operations and maintenance.  

Examples of the products we have recently been requested to provide spares solutions and repairs services include Motorola Desk Radio Terminals: 

Terminal Products
Part NumberProduct CodeDescription
M47PCC6T25_NMT912MTM700 380-430 MHz DESK Terminal
M80PCC6TZ5_NMT912MMTM800 380-430 MHz DESK Terminal
FIRMWARECLEAR / TEA1 / TEA2Choice for all radios
OPTIONEXP DASHExpand Control Head, 5m cable

If you have similar or other Radio solutions requirements and legacy maintenance services needs, please get in touch to discuss how we may be of assistance.

Cable products

Cable solutions to fulfil bespoke requirements

Customers with deployed infrastructure networks require not only spares, repairs and support, but also cable products to ensure continued long-term operations and maintenance.  

@YellowsBestLtd is pleased to continue to provide bespoke solutions to meet exact requirements. These items are newly manufactured, specifically made to order.

Examples include cables for Nokia ‘Dynanet’ VF E&M interfaces and Bus Wire:

Cable Products
Part NumberProduct CodeDescription
006-22021236.10 Cable21236.10 3mtr 20pr foil/braid LSZH Cable P1 & P2

 

Part NumberProduct CodeDescription
580-512Bus Wire30AWG Solid core unshielded silver cable 8 pair – 50m

“Keeping Customers Operational”

If you have similar or other new cabling requirements, requirements for legacy infrastructure spares, repairs and maintenance support, please get in touch to discuss how we may be of assistance.

Celebrating 8 years of supporting Customers and supplying Services and Solutions

@YellowsBestLtd has been assisting with “Keeping Customers Operational” for eight years now. Over the time we have been in business, we have supported our Customers with Services and Solutions.

We provide a range of Business Development professional Services, such as Consultancy and Value Added Resale.

We help Customers to keep their infrastructure networks operational by undertaking a range of Enterprise Support activities, including O&M, training and Reverse logistics.

We ensure Sustainable Systems by sourcing Solutions to assist customers maintain the operational status of their infrastructure.

We support deployed systems by providing hardware repair and software corrections and suppling spares or functional replacements.

We offer various new and ‘legacy’ equipment Technologies and a wide range of infrastructure, telecoms and other Products, seeking out new, surplus and refurbished equipment spares equipment cards, as well as supplying built-to-order cables and connectors to suit exact requirements.

The Market Sectors of the diverse organisations we assist include Utilities, Transport and Private and Public Operators who operate and maintain their own network infrastructure, providing them with Solutions to do more whilst reaping cost-benefits.

We hope to continue to be of assistance for many further years. Please contact us to let us know how we can assist you to keep your systems operational . We look forward to hearing from you.

Professional CCTV Cameras

Many business operations depend on the security delivered by professional standard CCTV cameras, offering reliability, availability and a wide range of advanced features for mission-critical surveillance applications. One manufacturer that provides an extensive range of such products is Bosch; one of their latest models we feature here.

Bosch MIC IP Starlight 7100i Outdoor PTZ

This example of a robust PTZ IP camera is suitable for deployment in extreme outdoor locations that require reliable 24-hour security monitoring. It features a range of advanced imaging technologies as well as Bosch’s Intelligent Video Analytics.

Featuring a 1/2″ 2MP CMOS sensor and a 6.6-198mm motorized zoom lens, the camera captures video at resolutions up to 1920 x 1080 at 60 fps in a 58.3 to 2.1° field of view. The camera delivers color video in lighting conditions as low as 0.0047 lux and uses an automatic IR cut filter to switch from color to B&W for day/night functionality.

An integrated high-speed pan/tilt system with an anti-backlash drivetrain provides 360° continuous panning and 290° tilting at up to 120° and 90° per second, respectively. Housed in an IP68- and IK10-rated enclosure and equipped with a window defroster, the camera is suitable for use in vandal-prone outdoor locations. Audio input and output ports allow for two-way talk while an SD card slot enables onboard storage of footage. ONVIF compliance ensures compatibility with a wide range of surveillance devices.

Solutions for New and Legacy Product Sources and Supply

@YellowsBestLtd seeks out new products and legacy equipment spares to assist with our aim of “Keeping Customers Operational“. Recent enquiries have included not only CCTV cameras, but also the supplying refurbished and surplus stocks of equipment cards, as well as built-to-order cables and connectors to suit exact requirements. Please get in touch to discuss any solutions or services requirements that you have; we look forward to hearing from you!

GAIA – Earth Artwork by Luke Jerram

Fortunate to see the display of Gaia, the touring artwork by UK artist, Luke Jerram, hosted this month at the Beverley Minster.

Measuring seven metres in diameter and created from detailed NASA imagery of the Earth’s surface the artwork provides the opportunity to see our planet, floating in three dimensions. In Greek Mythology Gaia is the personification of the Earth.

Common features of the experience are a feeling of awe for the planet, a profound understanding of the interconnection of all life, and a renewed sense of responsibility for taking care of the environment.

@YellowsBestLtd helps Customers with their operational needs, and one aspect is to #Reduce the demand for avoidable whole-scale replacements through a combination of supply for #Reuse of refurbished spares and repair of system elements. When removal and disposal of no-longer serviceable infrastructure parts is necessary, we can also assist with the resale and #Recycle for ‘value recovery’ of valuable materials. In this small way, we aim to make a difference in the impact we have on our planet through sustainable solutions.

Please get in touch should you wish to discuss your operational requirements and see how @YellowsBestLtd can be of assistance.

New parts for Legacy systems

Keeping Customers Operational

A continuing challenge for public and private network owners is the ongoing maintenance of infrastructure systems to support their business needs. In many cases, it makes sense to continue to operate legacy systems which are still fulfilling unchanged requirements, rather than contemplate costly and time-consuming change-outs and replacements.

@YellowsBestLtd seeks out new products and legacy equipment spares to assist with these aims. Recent enquiries have been fulfilled supplying refurbished and surplus stocks of equipment cards, as well as built-to-order cables and connectors to suit exact requirements.

There follows a few examples of items we have recently supplied. We would welcome any enquiries for the supply of similar or alternative parts, or support services to provide hardware repairs. Please get in touch; we look forward to hearing from you!

Example items, recently supplied

Connectors
Part NumberProduct CodeDescription
D-21470EuroEuro Connector 3×7
Connector 3×7 – D-21470
Connector 3×7 – D-21470
Cables
Part NumberProduct CodeDescription
102-722-1Coax-SMB 1mBT3002 Coax Cable BNC Plug to SMB Right Angle, 1m
102-722-3Coax-SMB 3mBT3002 Coax Cable BNC Plug to SMB Right Angle, 3m
102-722-5Coax-SMB 5mBT3002 Coax Cable BNC Plug to SMB Right Angle, 5m

Coax-SMB-5m

Equipment
Part NumberProduct CodeDescription
T37882.02NDUeNDM DC Unit
TA 21513DF 2-8Term. Repeater 2-8 M, 1300nm LED MM/SM
TU 21236.10VF E&MCU 8ch E&M/uP: 1xUKe&m/VF
TU 21216SUB/EXCHChannel Unit SUB/EXCH
SUB/EXCH – TU 21216

More equipment spares are listed here

Motherboard Repairs

Repairs to elements such as modules and cards of infrastructure hardware is one way we achieve our mission of “Keeping Customers Operational”. A good and recent example is Motherboards for display systems. These are from established, long-standing and therefore proven and fit-for-purpose systems. It therefore makes sense to maintain and extend the life of these parts.

Typical with such ‘legacy’ elements is that the level of complexity of the items is not excessive, meaning that repairs using discreet components is perfectly feasible, unlike more modern integrated systems which use specialised parts that cannot be freely or cheaply obtained or impossible to disassemble resulting in them being classed as ‘BER’ (Beyond Economic Repair). This is ultimately costly and disruptive, requiring wholesale replacements.

@Yellowsbestltd would be keen to hear from you should you have any repairs requirements. We would welcome receiving any defective items you have in order to perform a no-cost assessment to establish the feasibility and likely cost of restoration. Please get in touch to let us know how we can help.