Keep Legacy Systems Running with a DO-254 HDLC & SDLC Part Replacement IP Core
03/19/2025 - 08:17
One not-so-glamorous but vitally important use for CAST digital IP cores is to replace obsolete parts. Many of our cores can provide the answer if you’re maintaining a legacy system and need to make your own FPGA for a discrete part that was discontinued years ago, or perhaps consolidating a working but ancient board design into a single new chip.
Several of our cores are excellent part replacement solutions, offering direct drop-in ease and backwards compatibility, or — with minor code or system design changes — can easily expand legacy functionality or improve performance. The 8051 MCU is one example, a 45-year-old architecture that continues to function in many systems and can even serve a role in modern designs. (OurL8051XC1 Legacy-Configurable 8051 is especially well-suited to parts replacement.)
HDLC (High-Level Data Link Control) and SDLC (Synchronous Data Link Control) are bit-oriented protocols that provide error detection, flow control, and data framing for reliable data communication. They are old: IBM developed SDLC in 1975 for its Systems Network Architecture (SNA) traffic, and the expansion of SDLC to HDLC became an ISO standard in 1979. While these have been upstaged by Ethernet-based (TCP/IP and UDP/IP) and other newer protocols, they have proven their reliability and robust error correction in many thousands of systems and are still in use today.
HDLC is used in networking applications — e.g., cellular base station controllers, frame relay switches, and high-bandwidth WAN links — and in the mission-critical domain it remains important for military communication systems that require error resiliency such as tactical data links and satellite communications.
SDLC is employed in legacy aeronautic and industrial control systems (and, of course, some IBM Mainframe Systems).
Most suppliers stopped producing discrete parts for these protocols years ago. If you need to replace one today‚ such as the Zilog Z85230 or Motorola MC68302 for HDLC, you might find a distributor with a stash of existing parts somewhere. But the smarter approach can be to replace it using an HDLC or SDLC IP core.
CAST’s HSDLC Core for Parts Replacement
CAST HSDLC IP Core:
Flexible Frame Customization Features
Programmable preamble pattern and preamble length
NRZ, NRZI-Space, NRZI-Mark, Manchester, and Bi-Phase Space Data Coding
Programmable interframe space
Automatic BOF/EOF fields
Single- and double-byte address field
CRC-16 initialization value can be programmable or constant
Supports disabling address checking
Modem control (RTSn/CTSn)
Collision detection
Our HSDLC core has been used in many customer projects since our first sale in 2014. It’s an excellent choice for any new system needing HDLC or SDLC functionality. It’s also one of the very best available IP cores for obsolete parts replacement thanks to its proven reliability, low integration friction, and several standout features:
It works with a wide range of legacy systems and both the HDLC and SDLC protocols,
Its extensive programmable features provide the flexibility to match proprietary frame formats and other specific legacy requirements (see table),
It can provide robust performance, especially in ASICs, making it suitable for demanding applications, and
Integrating it with either legacy or modern systems is straightforward, using a generic 80C51-like bus interface or the AMBA® APB or AXI4-Lite interfaces to internal registers.
Most important for many mission-critical defense, aeronautic, space, railroad, and other safety-first applications, the HSDLC Core is available in a Safety Enhanced, DO-254 certified version.
While retaining legacy compatibility, this optional DO-254 version enhances earlier architectures with triple modular redundancy (TMR) for all internal registers. This makes the SDLC/HDLC core largely immune to single-bit upsets and errors, and it is able to comply with the stringent Design Assurance Level A (DAL-A) of the DO-254 standard. The core is also delivered with a complete DO-254 Certification Data Package, so you are ready to get your end product certified to this level.
This is just one of the several cores we offer for Functional Safety. If the SHDLC might be a solution for your legacy maintenance or new system design challenges, let us know and we’ll see how we can help.
And keep that legacy military or other system running!
