The History of the SLC-500
The History of the SLC-500
SLC full name is “Small Logic Controller”. The first SLC, Known simply as an SLC500, was an integrated platform containing the CPU, power supply, and IO all in one package. with 1K of memory and was used in small i/o application
SLC500: In 1991 Allen-Bradley released the first SLC500. This platform was physically smaller and less expensive than the PLC5, with a reduced instruction set nearly identical to the PLC-5.
The first rack-based SLC was the SLC5/01. This processor was used in a rack with power supply. The I/O cards also available in a rack.
Different type of i/o card having digital, analog and special purpose I/O such as thermocouples and High-Speed Counters. Processors had more memory, faster speeds, and enhanced communication capabilities.
The 5/02 and 5/03 platforms had DH485 (“Data Highway”) communications. The 5/03 was the first processor where logic could be edited online in real time without having to place the processor in program mode and download.
The 5/04 had even more memory and a faster communications platform called DH+ (“Data Highway Plus”).
The 5/05 had a serial port but also was the first to provide Ethernet communications.
A more detailed description and development of SLC-500 family of Programmable Logic Controllers
The 5/01 and Fixed Controllers: Modular and Brick
The first controller to come out for SLC-500 modular systems was the 5/01.
It launched in a 1K memory version (1747-L511,) which was quickly followed by a 4K version (1747-L514.)
While the L514 used battery backed memory, the L511 had capacitor backed memory with the option to use a battery.
Both 5/01 models were said to be capable of controlling up to 3840 digital I/O points across a maximum of 3 I/O Chassis and 30 I/O Slots.
These processors had an average scan time of 8ms per 1K of program and supported 52 Ladder Logic instructions.
They both came with a DH-485 programming port that accepted an RJ45 style connector, a connector most readers today will associate with Ethernet cables.
It’s important to note that all SLC-500’s with a native DH-485 RJ45 style port also provide power via that port for accessories like the original Hand Held Programmer (1747-PT1) as well as the DH-485 Link Coupler (1747-AIC.)
Note: Please avoid plugging Ethernet device into SLC-500 DH-485 ports as it could damage your device and/or SLC.
SLC-5/01s could be programmed through their DH-485 port using either a Hand Held Terminal (a 1747–PTA1E installed in a 1747–PT1) or the SLC-500 version of Rockwell’s 6200 software known as APS (Advanced Programming Software, 1747-PA2E.)
Icom also release a version of it’s popular A.I. (Advanced Interface) programming software for the SLC-500, called “PLC–500 A.I. Series Software.”
While the 5/01 could communicate over a DH-485 network, it was only able to “respond” to messages sent it from either a PC or future SLC-500 controllers (5/02, 5/03, etc.)
As far as the Fixed SLC-500’s are concerned, they shared all the same specs as the 1747-L511, except each had a limited number of build-in I/O points and accepted a single two slot I/O expansion chassis.
The 5/02: Faster and with more power
The next SLC-500 controller to come out was the SLC-5/02.
This processor was similar to the L514 as it had 4K of battery backed memory and a DH-485 communications port.
But it differed from the L514 in that it executed its programs much faster (4.8ms/K,) and could initiate DH-485 network messages as well as respond to them.
The 5/02 also supported up to 4096 I/O points across 3 chassis and 30 slots.
But the biggest new features of the 5/02 included it’s 19 additional ladder logic instructions, one of which was the first iteration of a SLC-500 PID instruction.
The 5/02 was also the first SLC-500 to support Indexed Addressing, Interrupts, User Fault Routines, and the ability to handle 32-bit signed math functions.
The 5/03: Editing online and more
In my opinion, the SLC-500 really hit its stride with the release of the SLC-5/03.
This was the first SLC-500 to incorporate many of the PLC-5’s features including Online Programming and Editing, as well as a Run Mode Switch on the face of the controller.
And in addition to the DH-485 port, it also had a user-friendly RS-232 9 Pin D-Shell port which could be used for programming via the DF1 Full Duplex protocol, or used in SCADA Master/Slave systems with DF1 Half Duplex protocol, or used with ASCII instructions to read and write to ASCII devices like Bar Code Readers and Serial Printers.
While the 5/03 initially only came in a 16K version (L532,) over time an 8K (1747-L531) and 32K (1747-L533) were added to the product line.
All three models had battery backed memory, and an average scan time of 1ms per 1K or program.
The SLC-5/03 controllers also included a real-time clock, 2MS STI (Selectable Timed Interrupt) .5ms DII (Discrete Input Interrupt), as well as true Indirect Addressing.
As far as instructions, the SLC-5/03 supported 99, including advanced math features like trigonometric and exponential instructions, as well as a more advanced PID instruction.
The 5/03’s were also the first SLC-500s to support upgrades through flash firmware, as well as new instructions like the CPT “Compute” instruction, and support for the Floating Point data type (i.e. F8:0.)
The 5/04: Data Highway Plus
As the SLC-500 become more popular, many facilities wanted to add them to their existing Data Highway Plus networks (as opposed to building a second DH-485 network.)
With that in mind, the SLC-5/04 was born.
Nearly identical to the SLC-5/03, the 5/04 came with a Data Highway Plus (DH+) port in place of a DH-485 port, and it supported all three DH+ baud rates (57.6K, 115.K, and 230.4K.)
Note: If you’re thinking that should be 56K and not 57.6K, you’re not alone! Many people get that DH+ baud rate mixed up with the fast 56K dial-up modems of the time
The SLC-5/04 would also eventually come in three memory sizes: 16K (L541,) 32K (L542,) and 64K (L543.)
Aside from being slightly faster than the SLC-5/03 by scanning 1K of program in just .9ms, most all of the other 5/04 specs are the same as the 5/03.
The 5/05: Ethernet
As Rockwell’s own documentation states, the SLC-5/05 provides identical functionality as the SLC-5/04, but with an Ethernet Port in place the DH+ port.
Initially the 5/05’s 10BaseT RJ45 Ethernet Port only supported 10Mbps, but with the release of the Series C hardware, Rockwell added 100 Mbps support as well.
Diagram of the SLCs from beginning to last.