The CompactLogix family of Programmable Automation Controllers has been popular with Small Machine Builders and System Integrators for many years.
The First Generation of CompactLogix Controllers: You can have any communications port you want, as long as it's serial.
While initially there was a lot of interest in these controllers, the number of actual applications suited to their reduce memory and “serial only” communication ports was limited.
The 1769-L20 controller had 64K of memory, a single Serial Port, and supported up to 8 I/O modules across a maximum of two I/O banks connected via a single expansion cable.
The 1769-L30 controller had 256K of memory, two serial ports, and supported up to 16 I/O modules across a maximum of three I/O banks connected by up to two expansion cables.
In both cases, the controller needed to be the “left most” device in the first I/O bank, and the controller also needed to be within four modules of power supply.
Similar to some of the MicroLogix controllers, the L20 and L30 both included a “default communications” button.
Pressing this button would return Channel 0 to the default settings shown below:
- Source ID / Node Address: 0
- Baud Rate” 19.2K
- Data Bits: 8
- Parity: None
- Stop Bits: 1
- Error Detection: BCC
- Protocol: DF1 point-to-point (Full Duplex)
- Control Lines: No handshaking
But unlike MicroLogix controllers with this feature, the L20 and L30's “default communications” button did not toggle between User and Default Settings.
Instead, when the L20 and L30's “default communications” button was pressed (and the Green “DCH0” LED came on,) any Channel 0 User Settings were replaced with the Default Settings.
This meant that the only way to return the controller to the original User Settings was to either (1) download the original program, or (2) make the changes online using RSLogix 5000.
The actual “default communications” button is accessed via a “pin hole” located on the bottom right front of the controllers, and to press it you'll need a non-conductive, pin sized object.
To access the battery compartment, users simply slid the left side of the controller forward, revealing the battery connector and clip on the controller's circuit board.
Using RSLogix 5000, programs could be saved to (or loaded from) the on-board non-volatile memory, as well as set to load automatically on power-up or when the battery backed (volatile) memory was corrupt.
In the end, even though the first generation of CompactLogix controllers had its share of limitations, it did pave the way for the next generation of CompactLogix controllers, including the very popular 1769-L32E and 1769-L35E.
So, do you ever use the first gen L20 or L30?
And if you did, what did you think of them at the time?
You can share your thoughts and opinions with us by clicking on the comment link below my signature.
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